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THE   COMPENDIOUS  MANUAL 


Qualitative  Chemical  Analysis 


OP 


C.  W.  ELIOT  AND  F.  H.   STORER 


AS  REVISED  BY  W.  R.  NICHOLS 


SIXTEENTH   EDITION 


NEWLY  REVISED 
By  W.  B.  LINDSAY,  A.B.,  B.S. 

Professor  or  Chbmistby  in  Dickinson  Colliob 


NEW  YORK 
D.  VAN   NOSTRAND   COMPANY 

23  Murray  Street  and  27  Warren  Street 

1892 


1^ 


Copyright,  1891, 
Bt  O.  W.  ELIOT,  F.  H.  STOKER,  and  F.  W.  NICHOLS. 


Ttpoorapht  bt  J.  S.  CusHiNQ  &  Co.,  Boston. 


D 


PREFACE. 


The  authors  have  endeavored  to  inchide  in  this  short  treatise 
enough  of  the  theory  and  practice  of  qualitative  analysis  "  in  the 
wet  way,"  to  bring  out  all  the  reasoning  involved  in  the  subject, 
and  to  give  the  student  a  firm  hold  upon  the  general  principles  and 
methods  of  the  art.  It  has  been  their  aim  to  give  only  so  much 
of  mechanical  detail  as  is  essential  to  an  exact  comprehension  of 
the  methods  and  to  success  in  the  actual  experiments.  Hence,  the 
multiplication  of  different  tests  or  processes,  having  essentially  the 
same  object,  has  been  purposely  avoided.  For  the  same  reason  none 
of  the  rare  elements  are  alluded  to.  The  manual  is  intended  to 
meet  the  wants  of  the  general  student,  to  whom  the  study  is  chiefly 
valuable  as  a  means  of  mental  discipline  and  as  a  compact  example 
of  the  scientific  method  of  arriving  at  truth.  To  professional  stu- 
dents who  wish  to  make  themselves  expert  analysts,  this  little  book 
offers  a  logical  introduction  to  the  subject,  an  outline  which  is 
trustworthy  as  far  as  it  goes,  but  which  needs  to  be  filled  in  and 
enlarged  by  the  subsequent  use  of  some  more  elaborate  treatise  as  a 
book  of  reference.  Professor  Johnson,  of  Yale,  has  supplied  this  need 
with  his  excellent  edition  of  Fresenius's  comprehensive  manual. 

The  authors  believe  that  they  have  put  into  the  following  pages 
as  much  of  inorganic  qualitative  analysis  as  is  useful  for  training, 
and  also  as  much  as  the  engineer,  physician,  agriculturist  or  liber- 
ally educated  man  needs  to  know.  The  book  has  been  written  for 
the  use  of  classes  in  the  Institute  of  Technology,  who  have  already 
studied  the  authors'  "Manual  of  Inorganic  Chemistry."  It  is 
simply  an  implement  devised  to  facilitate  the  giving  of  thorough 
instruction  to  large  classes  in  the  laboratory.  It  is  the  authors' 
practice  to  examine  their  classes  orally  every  four  or  five  exercises, 
in  order  to  secure  close  attention  to  the  reasoning  of  the  subject. 

iii 


iv  PREFACE. 

With  this  exception,  the  subject  is  studied  exclusively  in  the  labo- 
ratory, tools  ill  hand.  Fifty  laboratory  exercises  of  two  hours  each 
have  proved  sufficient  to  give  their  classes  a  mastery  of  the  subject 
as  it  is  presented  in  this  manual. 

It  is  scarcely  necessary  to  say  that  this  little  work  is  a  compila- 
tion from  well-known  authorities,  among  which  may  be  particularly 
mentioned  the  works  of  Galloway,  Will,  Fresenius,  and  Northcote 
&  Church. 

Boston,  April,  1869. 


PREFACE  TO  THE  REVISED  EDITION. 

In  this  revised  edition,  undertaken  with  the  advice  and  consent 
of  the  authors,  such  alterations  and  additions  have  been  made  as 
have  been  suggested  by  the  use  of  the  book  with  a  number  of 

classes  in  the  laboratory. 

W.  R.  NICHOLS. 
BosToy,  July,  1876. 


PREFACE  TO  THE  PRESENT  EDITION. 

This  edition  has  been  carefully  revised  with  the  co-operation  of 

Professor  F.  H.  Storer.     The  alterations  and  additions  are  such  as 

an  experience  of  several  years'  use  of  the  book  has  suggested,  and 

it  is  hoped  will  add  to  its  utility. 

W.   B.   LINDSAY. 

Dickinson  Collbge, 
Carlisle,  Penn.,  November,  1891. 


TABLE  OF   CONTENTS. 


PAGB 

Introduction.     Qualitative  analysis  defined.     Scope  of  this 

manual.    Identifying  compounds.    Division  of  the  subject. .      1-4 

PART  I. 

Chapter  I.  Example  of  the  separation  of  two  elements.  Di- 
vision of  twenty-four  metallic  elements  into  seven  classes. . .     5-18 

Chapter  II,    Class  I.     Chlorides  insoluble  in  water  and  acids. 

Lead.    Silver.    Mercury 19-22 

Chapter  III.  Class  II.  Sulphides  insoluble  in  water,  dilute 
acids  and  alkalies.  Mercury.  Lead.  Bismuth.  Copper. 
Cadmium.     The  precipitation  of  Classes  II  and  III 23-31 

Chapter  IV.  Class  III.  Sulphides  insoluble  in  water  or  dilute 
acids,  but  soluble  in  alkaline  solutions.  Arsenic.  Anti- 
mony. Tin.  Gold  and  platinum.  Separation  of  Classes 
II  and  III 32-45 

Chapter  V.  Class  IV.  Hydrates  insoluble  in  water,  ammo- 
nia-water and  solutions  of  ammonium  salts.  Simultaneous 
precipitation  of  some  salts  which  require  an  acid  solvent. 
Treatment  of  the  precipitate  produced  by  ammonia-water. 
Chromium.  Aluminum.  Manganese.  Iron.  Separation 
of  Class  IV  from  Classes  II  and  III.  The  original  condition 
of  iron.  The  use  of  chloride  of  ammonium.  Interference  of 
organic  matter 46-57 

Chapter  VI.  Class  V.  Sulphides  insoluble  in  water  and  in 
saline  or  alkaline  solutions.  Manganese.  Zinc.  Nickel. 
Cobalt.    Separation  of  Class  V  from  Class  IV 68-64 

V 


VI  CONTENTS. 

FAOE 

Chapter  VII.  Class  VI.  Carbonates  insoluble  in  water, 
ammonia-water  and  saline  solutions.  Barium.  Strontium. 
Calcium.  Separation  of  Class  VI  from  the  preceding 
classes 65-70 

Chapter  VIII.  Class  VII.  Three  common  metallic  elements 
not  comprised  in  the  preceding  classes.  Magnesium. 
Sodium.  Potassium.  Table  for  the  separation  of  the 
seven  classes  of  the  metallic  elements 71-75 

Chapter  IX.  General  tests  for  the  non-metallic  elements. 
The  classes  of  salts  treated  of.  General  reactions  for  acids. 
Metallic  elements  to  be  first  detected.  The  barium  test. 
The  calcium  test.  The  silver  test.  Nitrates,  chlorates 
and  acetates 76-86 

Chapter  X.  Special  tests  for  the  non-metallic  elements. 
Effervescence.  Carbonates,  Cyanides.  Sulphides.  Sul- 
phites. Hyposulphites  (Thiosulphates).  Chromates.  Ar- 
senites  and  Arseniates.  Sulphates.  Phosphates.  Oxalates. 
Borates.  Silicates.  Fluorides.  Chlorides.  Bromides. 
Iodides.  Nitrates.  Chlorates.  Acetates.  Oxides  and 
Hydrates 87-104 

PART  II. 

Treatment  of  Substances  of  Unknown  Composition.  Gen- 
eral observations.    Husbanding  material 105 

Chapter  XI.  Treatment  of  a  salt,  mineral  or  other  non- 
metallic  solid.  Order  of  procedure.  .  .  .  Preliminary  ex- 
amination in  the  dry  way.  Closed-tube  test.  Gases  or 
vapors  to  be  recognized.  Sublimates.  Reduction  test. 
Metallic  globules.  .  .  .  Dissolving  a  salt,  mineral  or  other 
non-metallic  solid,  free  from  organic  matter.  Dissolving 
in  water.  Dissolving  in  acids.  .  .  .  Treatment  of  solutions 
obtained.  An  aqueous  solution :  neutral,  acid,  alkaline. 
An  acid  solution.  .  .  .  Examination  of  the  solutions  for 
the  non-metallic  elements.  .  .  .  Table  of  solubilities.  .  .  . 
Treatment  of  insoluble  substances.  Fusions.  Treatment 
of  the  fused  mass.  Decomposition  by  means  of  carbonate 
of  calcium  and  chloride  of  ammonium.  Fusion  with  acid 
sulphate  of  sodium.    Deflagration 106-140 


CONTENTS.  Vll 


Chapter  XII.    Treatment  of  a  pure  metal  or  alloy.     Action 

of  nitric  acid  on  metals.    Gold  test.    Platinum  test 141-144 

Chapter  XIII.    Treatment  of  liquid  substances.    Evapora- 
tion test.    Testing  with  litmus.    Testing  for  ammonia. ...  146,  146 


APPENDIX. 

Reagents.  Acids.  Sulphuretted  hydrogen.  Ammonia-water. 
Ammonium  salts.  Sodium  hydrate.  Sodium  salts.  Potas- 
sium salts.  Iodide  of  potassium  and  starch  papers.  Nitrate 
of  silver.  Slaked  lime.  Lime-water.  Calcium  chloride. 
Barium  salts.  Acetate  of  lead.  Lead  paper.  Magnesium 
solution.  Ferric  chloride.  Nitrate  of  cobalt.  Sulphate 
of  copper.  Stannous  chloride.  Oxide  of  manganese. 
Mercury  salts.  Platinic  chloride.  Zinc.  Solution  of 
indigo.  Litmus  paper.  Starch.  Alcohol.  Water.  Hypo- 
chlorite of  sodium.  Bisulphide  of  carbon.  Chlorine 
water 149-158 

Solutions  of  Known  Composition 169-161 

Utensils.  Reagent-bottles.  Test-tubes.  Test-tube  rack. 
Flasks.  Beakers.  Glass  funnels.  Filtering.  Filter-stand. 
Rapid  filtration.  Porcelain  dishes  and  crucibles.  Lamps. 
Blast-lamps  and  blowers.  Iron-stand.  Tripod.  Wire- 
gauze.  Triangle.  Water-bath.  Sand-bath.  Blowpipes. 
Platinum  foil  and  wire.  Pincers.  Platinum  crucibles. 
Wash-bottle.  Glass  tubing.  Stirring-rods.  Cutting  and 
cracking  glass.  Bending  and  closing  glass  tubes.  Blowing 
bulbs.  Caoutchouc.  Corks.  Gas-bottle.  Self-regulating 
gas-generator.    Mortars.    Spatulae 162-197 


QUALITATIVE  ANALYSIS. 

INTRODUCTION. 

1.  Qualitative  Analysis,  in  the  widest  sense  of  the  term, 
is  the  art  of  finding  out  the  elements  contained  in  com- 
pound substances.  This  general  definition  has  important 
limitations  in  practice.  In  the  first  place,  the  art,  as  com- 
monly taught,  applies  almost  exclusively  to  mineral,  or  in- 
organic, substances,  and  touches  only  incidentally  upon  the 
multifarious  compounds  of  carbon  with  hydrogen,  oxygen, 
nitrogen  and  a  few  other  elements,  which  form  the  subject- 
matter  of  that  branch  of  chemical  science  called  organic 
chemistry.  Again,  the  analysis  of  gases  constitutes  a  dis- 
tinct branch  of  analysis,  requiring  methods  and  apparatus 
of  its  own,  and  therefore  to  be  most  advantageously  studied 
by  itself.  These  deductions  made,  there  remains  the  analy- 
sis of  inorganic  solids  and  liquids,  which  is  in  fact  the  main 
subject  of  qualitative  analysis  in  the  present  technical  sense 
of  the  term. 

Only  the  more  important  chemical  elements  are  embraced 
in  the  systematic  course  of  this  manual.  Means  of  detect- 
ing a  few  less  common  elements  are  incidentally  given. 
Those  of  the  elements  which  are  so  rare  as  to  be  at  present 
of  little  interest  except  to  the  professional  chemist  or  min- 
eralogist are  not  alluded  to. 

1 


2  IDENTIFYING   COMPOUNDS.  [§§2,3. 

2.  Some  previous  knowledge  of  general  chemistry  is  es- 
sential to  the  successful  study  of  qualitative  analysis.  It 
is  assumed  that  the  student  knows  something  of  the  com- 
mon elements  and  of  their  most  important,  combinations, 
that  he  is  familiar  with  the  principal  laws  which  govern 
chemical  changes,  and  that  he  possesses  a  certain  skill  in 
the  simplest  manipulations.  The  tools  and  operations  em- 
ployed in  qualitative  analysis  are  few  and  simple ;  but  neat- 
ness, method  in  working  and  a  vigilant  attention  even  to 
the  minutest  details,  are  absolutely  essential.  As  the  vari- 
ous substances  used  or  produced  in  the  operations  of  analy- 
sis will  not  be  particularly  described,  the  careful  student 
will  keep  at  hand  some  text-book  on  general  chemistry,  to 
which  he  can  constantly  refer  to  refresh  his  recollection  of 
the  formulae  and  physical  and  chemical  properties  of  the 
substances  referred  to.  It  should  be  observed  that  it  is 
often  very  difficult  —  in  fact,  impossible  in  the  present  state 
of  knowledge  —  to  express  in  exact  equations  the  involved 
or  obscure  reactions  which  occur  in  complex  mixtures  dur- 
ing the  operations  of  analysis.  It  is  a  useful  exercise  for 
students  to  write  out  in  equations  the  simpler  chemical 
changes  which  occur  in  analysis ;  but  when  the  attempt  is 
made  to  put  a  complex  reaction  into  numerical  symbols, 
the  equations  are  apt  to  express  either  more  than  we  know, 
or  less. 

3.  Although  the  detection  of  the  elements  contained  in 
compound  substances  is  the  ultimate  object  of  analysis,  it 
is  only  by  exception  that  the  elements  themselves  are  iso- 
lated, and  recognized  in  their  uncombined  condition.  An 
element  is  generally  recognized  through  some  familiar  com- 
pound, whose  apparition  proves  the  presence  of  all  the  ele- 
ments it  contains,  just  as  the  presence  of  any  word  upon 
this  page  makes  it  sure  that  the  letters  with  which  it  is 
spelt  are  imprinted  there.     If,  as  the  result  of  a  definite 


§  3,  4.]  IDENTIFYING   COMPOUNDS.  3 

series  of  operations  upon  some  unknown  body,  the  hydrated 
oxide  of  iron  be  produced,  no  iron  having  been  added  dur- 
ing any  stage  of  the  process,  the  proof  of  the  presence  of 
iron  in  the  original  body  is  quite  as  certain  as  if  the  gray 
metal  itself  had  been  extracted  from  it.  If  some  well- 
known  sulphate,  like  sulphate  of  lead,  or  of  barium,  for 
example,  result  from  a  series  of  experiments  upon  some 
unknown  mineral,  it  is  certain  that  the  mireral  contained 
sulphur ;  provided  only  that  no  sulphur  has  been  introduced 
in  any  of  the  chemical  agents  to  whose  action  the  mineral 
has  been  submitted. 

The  compounds  through  which  the  elements  are  recog- 
nized are  necessarily  bodies  of  known  appearance,  deport- 
ment and  properties.  They  are,  in  fact,  bodies  of  various, 
though  always  definite,  composition ;  oxides,  sulphides,  chlo- 
rides, sulphates  and  many  other  salts,  are  thus  made  the 
means  of  identifying  one  or  more  of  the  elements  which 
they  contain.  The  object  of  the  analyst  is  to  bring  out 
from  the  unknown  substance,  by  expeditious  processes  and 
under  conditions  which  admit  of  no  doubt  as  to  their  testi- 
mony, these  identifying  compounds,  with  whose  appearance 
and  qualities  he  has  previously  made  himself  acquainted. 
As  he  follows  the  course  of  experiments  laid  down  in  this 
manual,  the  student  will  gradually  acquire,  with  the  aid  of 
frequent  references  to  a  text-book  of  general  chemistry, 
that  stock  of  information  concerning  the  identifying  com- 
pounds which  must  be  always  ready  for  use  in  his  mind, 
and  at  the  same  time  he  will  be  made  familiar  with  the 
character  of  the  methodical  processes  which  secure  a 
prompt  and  sure  testimony  to  the  elementary  composition 
of  the  substances  he  examines. 

4.  The  subject  is  treated  in  two  parts  or  divisions,  of 
which  the  first  contains  a  series  of  experiments  to  illustrate 
a  systematic  course  of  examination  for  substances  in  solu- 


4  IDENTIFYING   COMPOUNDS. 

tion,  when  once  tliat  solution  has  been  made;  while  the 
second  treats  chiefly  of  the  preliminary  examination  of 
solids  and  the  means  of  bringing  them  into  solution,  and 
indicates  the  general  methods  to  be  pursued  in  the  actual 
analysis  of  a  substance  of  unknown  composition. 


Part  First. 

CHAPTER  I. 

DIVISION  OP   THE  METALLIC   ELEMENTS  INTO   CLASSES. 

5.  Example  of  the  Separation  of  two  Elements.  —  Put  a 
small  crystal  of  nitrate  of  silver  and  a  small  crystal  of  sul- 
phate of  copper  into  a  test-tube  (Appendix,  §  69),  and  dis- 
solve them  in  two  teaspoonfuls  (a  teaspoonful  is  equal  to 
five  cubic  centimeters)  of  water,  warming  the  water  at  the 
lamp  to  facilitate  the  solution.  Add  to  this  solution  a 
few  drops  of  dilute  hydrochloric  acid  (App.,  §  3).  Shake 
the  contents  of  the  tube  violently,  wait  until  the  curdy  pre- 
cipitate, which  the  acid  produces,  has  separated  from  the 
liquid,  and  then  add  one  more  drop  of  hydrochloric  acid. 
If  this  drop  produces  an  additional  precipitate,  repeat  the 
operation  until  the  new  drop  of  acid  produces  no  change  in 
the  partially  clarified  liquid.  Then,  and  not  till  then,  has 
all  the  silver  which  the  original  solution  contained  been 
precipitated  in  the  form  of  chloride  of  silver,  an  unemployed 
balance  or  excess  of  the  reagent,  hydrochloric  acid,  remain- 
ing in  the  clear  liquid ;  this  liquid  can  be  readily  separated 
by  filtration  from  the  curdy  chloride.  ^ 

Shake  the  contents  of  the  test-tube,  and  transfer  them 
as  completely  as  possible  to  a  filter  (App,,  §  74),  supported 
in  a  very  small  glass  funnel  (App.,  §  73),  which  has  been 
placed  in  the  mouth  of  the  test-tube .  With  a  wash-bottle 
(App.,  §  85)  rinse  into  the  filter  that  portion  of  the  precip- 
itate which  has  adhered  to  the  sides  of  the  first  test-tube. 

5 


6  THE  TEEM  '' CLASS.''  —  CLASS  L         [§§  5,6. 

When  the  filtrate  has  drained  completely  from  the  precipi- 
tate, set  the  test-tube  which  has  received  it  aside.  Wash 
tlie  precipitate  together  into  the  apex  of  the  filter  by  means 
of  a  wash-bottle  with  a  fine  outlet;  and,  in  order  to  wash 
out  the  soluble  sulphate  of  copper  which  adheres  to  the 
precipitate,  fill  the  filter  full  of  water  two  or  three  times, 
throwing  away  this  wash-water  when  it  has  passed  through 
the  filter. 

The  complete  separation  of  the  silver  and  copper  which 
were  mixed  in  the  original  solution  is  already  accomplished; 
the  silver  is  on  the  filter  in  the  form  of  chloride ;  the  cop- 
per is  in  the  clear,  bluish  filtrate.  This  speedy  and  effec- 
tual separation  of  the  two  elements  is  based  upon  the  fact 
that  chloride  of  silver  is  insoluble  in  water  and  acid  liquids, 
and  is,  therefore,  formed  when  hydrochloric  acid  is  added 
to  a  solution  containing  a  salt  of  silver;  chloride  of  copper, 
however,  is  readily  soluble  in  water  and  acid  liquids,  and, 
even  if  formed  by  the  addition  of  hydrochloric  acid  to  a 
solution  of  a  compound  of  copper,  would  fail  to  manifest 
itself  by  appearing  as  a  precipitate.  It  is,  in  general,  true 
that  whenever,  by  the  addition  of  a  reagent,  there  can  be 
formed  in  any  solution  a  compound  insoluble  in  the  liquids 
present,  this  compound  always  separates  as  a  precipitate. 
Such  differences  of  solubility  as  are  illustrated  by  the  case 
of  the  chlorides  of  silver  and  copper  are  the  chief  reliance 
of  the  analyst. 

6.  Definition  of  the  Term  "  Class."  Class  I.  —  In  the  forego- 
ing experiment  only  two  elements  have  been  separated.  It 
^ight  obviously  be  very  difficult,  if  not  impossible,  to  find 
a  special  reagent  for  every  element,  which  would  always 
precipitate  that  single  element  and  never  any  other.  Hy- 
drochloric acid,  for  example,  which  precipitates  silver  so 
admirably  from  any  solution  containing  that  element,  is 
capable  of  eliminating  two  other  elements  under  like  condi- 
tions.    The  lower  chloride  of  mercury  (mercurous  chloride 


§  6.]  DIVISION  INTO  CLASSES.        v  7 

or  calomel)  is  insoluble  in  water  and  weak  acids.  Chloride 
of  lead  is  sparingly  soluble  in  cold  water,  and  is  still  less 
soluble  in  water  acidulated  with  hydrochloric  acid.  The 
chlorides  of  the  other  metallic  elements  are  all  soluble  in 
water  and  acids  under  the  conditions  of  the  analytical  pro- 
cess. 

There  are  embraced  in  the  scope  of  this  manual  twenty- 
four  of  the  so-called  metallic  elements,  — elements  whose 
hydrates  or  oxides  are  said  to  be  basic  in  their  character, 
and  are  collectively  designated  as  bases:  if  hydrochloric 
acid  were  added  in  proper  quantity  to  a  solution  imagined 
to  contain  all  these  elements,  three,  and  only  three,  of  the 
twenty -four  elements  would  be  precipitated  as  chlorides. 
After  filtration  and  washing,  a  mixture  of  chloride  of 
silver,  chloride  of  lead  and  mercurous  chloride  would  re- 
main upon  the  filter,  and  all  the  other  elements  would  have 
passed  as  soluble  compounds  into  the  filtrate.  Silver,  lead 
and  mercury,  the  three  elements  thus  separated  from  the 
rest  by  this  well-marked  reaction  with  hydrochloric  acid, 
constitute  a  class,  the  first  of  several  classes  into  which  the 
metallic  elements  are  divided  for  the  ends  of  qualitative 
analysis.  Each  class  is  characterized  by  some  clear  reac- 
tion which  suffices,  when  intelligently  applied,  to  separate 
the  members  of  any  one  class  from  the  other  classes.  The 
chemical  agent,  by  means  of  which  this  distinctive  reaction 
is  exhibited,  is  called  the  general  reagent  of  the  class.  Thus, 
hydrochloric  acid  is  the  general  reagent  of  the  first  class. 

This  division  of  the  elements  into  the  classes  renders  it 
unnecessary  to  find  means  of  separating  each  individual 
element  from  all  the  others.  In  the  systematic  course  of 
an  analysis,  the  classes  are  first  sought  for  and  separated; 
afterwards  each  class  is  treated  by  itself  for  the  detection 
of  its  individual  members.  It  is  an  incidental  advantage 
of  this  division  of  the  elements  into  classes  that,  when  the 
absence  of  any  whole  class  has  been  proved  by  the  failure 


8  -^%         DIVISION  INTO  CLASSES.  [§§  6-8. 

of  its  peculiar  general  reagent  to  produce  a  precipitate  in 
a  solution  under  examination,  it  is  unnecessary  to  search 
further  for  any  member  of  that  class.  Much  time  is  thus 
saved,  for  it  is  as  easy  to  prove  the  absence  of  a  class  as 
of  a  single  element.  The  full  treatment  of  the  first  class  of 
elements,  comprising,  as  we  have  seen,  silver,  lead  and 
mercury,  is  the  subject  of  Chapter  II. 

7.  Experiment  to  Illustrate  the  Division  of  the  Metallic 
Elements  into  Classes.  —  We  proceed  to  demonstrate  experi- 
mentally the  chemical  facts  upon  which  rests  the  division 
of  the  other  metallic  elements  into  convenient  classes. 

Prepare  a  complex  solution,  by  mixing  together  in  a 
small  beaker  (App.,  §  72)  a  small  teaspoonful  of  each  of 
the  following  solutions  (App.,  §  66),  viz.:  —  chloride  of 
•^copper, "^rsenious  oxide  in  hydrochloric  acid,  ferrous  chlo- 
ride, chloride  of  zinc,  chloride  of  calcium,  chloride  of  mag- 
nesium and  chloride  of  sodium.  Dilute  the  mixture  thus 
prepared  with  its  own  bulk  of  water.  Should  any  turbidity 
or  precipitate  appear,  add  hydrochloric  acid,  little  by  little, 
until  the  solution  becomes  clear.  This  solution  is  repre- 
sentative ;  it  contains  at  least  one  member  of  each  of  the 
classes  of  elements  which  remain  to  be  defined.  It  con- 
tains no  member  of  the  first  class ;  but  we  may  consistently 
suppose  that  the  members  of  this  class  have  been  previously 
precipitated,  as  in  the  foregoing  experiment  (§  5),  and  that 
an  excess  of  hydrochloric  acid  remains  in  the  liquid. 

8.  Definition  of  Classes  II  and  in.  —  Pass  a  slow  current 
of  sulphuretted  hydrogen  (App.,  §  15)  from  a  gas-bottle  or 
self-regulating  generator  through  the  acid  liquid  in  the 
beaker.  This  operation  must  be  performed  either  out  of 
doors  or  in  a  current  of  air  sufficient  to  carry  the  excess  of 
the  gas  away  from  the  operator.  A  dense,  dark-colored 
precipitate  will  immediately  appear,  and  gradually  increase 
in  bulk.  When  the  gas  has  flowed  continually  for  five  or 
ten  minutes  through  the  liquid,  remove  the  beaker  from 


§  8.]  DEFINITION  OF  CLASSES  II  AND  fIL  9 

the  source  of  the  gas  (or  interrupt  the  stream  of  gas  if  a 
self -regulating  generator  be  employed),  stir  the  liquid  well, 
and  blow  out  the  sulphuretted  hydrogen  which  lies  in  the 
beaker.  If  after  the  lapse  of  two  or  three  minutes  the 
liquid  smells  distinctly  of  sulphuretted  hydrogen,  it  is 
saturated  with  the  gas,  and  it  is  sure  that  the  reagpnt  has 
done  its  work.  If  the  liquid  does  not  retain  the  character-' 
istic  odor,  the  gas  must  be  again  passed  through  it  until 
the  saturation  is  certainly  attained. 

In  order  to  obtain  still  further  assurance  of  the  satura- 
tion of  the  liquid,  it  is  often  well  to  take  the  first  portions 
of  the  filtrate  of  the  succeeding  paragraph  and  add  a  small 
quantity  of  sulphuretted  hydrogen  water  (App.,  §  16)  or 
pass  sulphuretted  hydrogen  through  it.  If  a  sufficient 
amount  of  gas  has  not  been  passed  into  the  liquid,  the  ad- 
dition of  the  sulphuretted  hydrogen  water  would  cause  the 
appearance  of  a  precipitate.  In  such  a  case  the  filtered 
portion  must  be  returned  to  the  beaker  and  the  stream  of 
gas  again  passed  through  the  liquid. 

Pour  the  contents  of  the  beaker,  well  stirred  up,  upon  a 
filter  which  is  supported  over  a  test-tube  or  second  beaker. 
Rinse  the  first  beaker  once  with  a  teaspoonful  of  water,  and 
transfer  this  rinsing  water  to  the  filter,  allowing  the  filtered 
liquid  to  mix  with  the  original  filtrate.    Label  ^  this  filtrate 

iThe  student  should  at  once  make  it  a  rule  to  label  every  filtrate  or 
precipitate  which  he  has  occasion  to  set  aside,  even  for  a  few  moments.  A 
bit  of  paper  large  enough  to  carry  a  descriptive  symbol  or  abbreviation 
should  be  attached  to  the  vessel  which  contains  the  liquid  or  precipitate. 
Paper  gummed  on  the  back,  or  the  small  labels  which  are  sold  already 
gummed,  are  convenient  for  this  use. 

This  habit,  once  acquired,  will  enable  the  studeut  to  carry  on  simul- 
taneously, without  error  or  confusion,  several  operations.  He  may  be 
throwing  down  one  precipitate,  washing  another,  filtering  a  third  and 
dissolving  a  fourth  at  the  same  time,  and  the  four  processes  may  belong  to 
as  many  different  stages  of  the  analysis.  There  will  be  no  danger  of  error 
if  labels  are  faithfully  used ;  and  a  great  deal  of  time  will  be  saved.  The 
unaided  memory  is  incapable  of  doing  such  work  with  that  full  certainty, 
admitting  of  no  suspicion  or  after-qualms  of  doubt,  which  is  alone  satisfy- 
ing, or  indeed  admissible,  in  scientific  research. 


10  ,.  S  CLASSES  II  AND  III.  [§  8. 

"  Filtrate  from  II  and  III "  (classes),  and  preserve  it  for 
later  study. 

If  any  considerable  quantity  of  precipitate  has  adhered 
to  the  sides  of  the  original  beaker,  it  may  be  detached  and 
washed  on  to  the  filter  by  means  of  a  sharp  jet  of  water 
from  the  wash-bottle.  The  precipitate,  as  it  lies  upon  the 
filter,  must  then  be  washed  once  or  twice  with  water ;  the 
wash-water  is  thrown  away.  The  washed  precipitate  con- 
sists of  a  mixture  of  sulphide  of  copper  (CuS)  and  trisul- 
phide  of  arsenic  (As^Sg) .  The  fact  that  these  sulphides  are 
precipitated  under  the  conditions  of  this  experiment  proves 
that  they  are  both  insoluble  in  weak  acid  liquors.  They 
are  also  both  insoluble  in  water.  But  an  important  differ- 
ence between  the  two  sulphides  nevertheless  exists,  a  differ- 
ence which  affords  a  trustworthy  means  of  separating  one 
from  the  other. 

When  the  water  has  drained  away  from  the  precipitate, 
open  the  filter  upon  a  plate  of  glass,  and  gently  scrape  the 
precipitate  off  the  paper  with  a  spatula  of  wood  or  horn. 
Place  the  precipitate  in  a  small  porcelain  dish  (App.,  §  77), 
pour  over  it  enough  of  a  solution  of  sulphide  of  sodium 
(App.,  §  24)  to  somewhat  more  than  cover  it,  and  heat  the 
mixture  cautiously  to  boiling,  stirring  it  all  the  time  with 
a  glass  rod.  The  quantity  of  sulphide  of  sodium  to  be 
employed  varies,  of  course,  with  the  bulk  of  the  precipi- 
tate; in  this  case  two  or  three  teaspoonfuls  will  probably 
suffice.  It  is  very  undesirable  to  use  an  unnecessarily  large 
quantity  of  the  reagent  for  reasons  that  will  h^eafter  ap- 
pear. A  portion  of  the  original  precipitate  remains  undis- 
solved ;  but  a  portion  has  passed  into  solution.  Filter  the 
hot  liquid  again.  The  black  residue  on  the  filter  is  sul- 
phide of  copper,  which  is  insoluble,  not  only  in  water  and 
weak  acids,  but  also  in  the  alkaline  sulphide.  To  the  filtrate, 
collected  in  a  test-tube,  add  gradually  hydrochloric  acid, 
until    the   liquid  has   an  acid  reaction  on   litmus   paper 


§8.]  MSRCUBT  AND  LEAD.  11 

(App.,  §  59).  A  yellow  precipitate  of  sulphide  of  arsenic 
will  appear  as  soon  as  the  alkaline  solvent  which  kept  it  in 
solution  is  destroyed.  The  sulphide  of  arsenic  differs  from 
the  sulphide  of  copper  in  that  it  is  soluble  in  alkaline 
liquids. 

In  this  series  of  experiments  copper  and  arsenic  stand, 
not  as  isolated  elements,  but  as  representatives  of  classes. 
The  following  common  elements  have  sulphides  which  are 
insoluble  in  water,  weak  acids  and  alkaline  liquids :  — 
Lead,  mercury,  bismuth,  cadmium  and  copper.  These 
elements  constitute  Class  II  in  our  system  of  analysis. 
The  following  elements  have  sulphides  which  are  insoluble 
in  water  and  weak  acids,  but  soluble  in  alkaline  liquids :  — 
Arsenic,  antimony,  tin  and  the  precious  metals  gold  and 
platinum.  These  elements  constitute  Class  III.  If  all 
the  elements  of  both  groups  had  been  present  in  the  original 
solution,  one  class  might  have  been  separated  from  the 
other  by  the  same  process  employed  in  the  case  of  the 
representative  elements,  arsenic  and  copper. 

The  question  may  naturally  suggest  itself,  how  it  hap- 
pens that  lead  and  mercury  are  included  in  Class  II,  when 
they  were  both  precipitated  in  Class  I.  The  chloride  of 
lead,  which  is  thrown  down  by  hydrochloric  acid,  is  not 
wholly  insoluble  in  water  or  dilute  hydrochloric  acid;  hence 
it  happens  that  the  lead  is  not  completely  precipitated  in 
Class  I.  That  portion  of  the  lead  which  has  escaped  pre- 
cipitation as  chloride  in  Class  I,  will  be  thrown  down  as 
sulphide  in  Class  II,  for  the  sulphide  of  lead  is  insoluble 
in  water,  weak  acids  and  alkalies.  In  regard  to  mercur^^ 
it  will.be  remembered  that  there  are  two  sorts  of  mercury 
salts,  mercurous  salts  and  mercuric  salts.  The  mercurous 
chloride,  HgCl  (calomel),  is  insoluble  in  water ;  but  the  mer- 
curic chloride,  HgCl.^  (corrosive  sublimate),  is  soluble  in  water. 
If,  therefore,  mercury  be  present  in  the  form  of  some  mer- 
curous salt,  it  will  be  separated  as  mercurous  chloride  in 


12  DEFINITION  OF  CLASS  IV.  [§§  8,  9. 

Class  I.  If,  on  the  contrary,  it  be  present  in  the  form  of 
some  mercuric  salt,  it  will  be  separated  in  Class  II  as  mer- 
curic sulphide  (HgS),  for  this  sulphide  is  insoluble  in  water, 
weak  acids  and  alkaline  liquids.  If  a  mixture  of  mercurous 
and  mercuric  salts  be  contained  in  the  original  solution, 
mercury  will  appear  both  in  Class  I  and  in  Class  II. 

The  treatment  of  Class  II  is  fully  discussed  in  Chapter 
III.  The  separation  of  Class  III  and  the  means  of  separat- 
ing the  members  of  the  class,  each  from  the  others,  form 
the  subject  of  Chapter  IV. 

9.  Definition  of  Class  IV.  —  We  now  return  to  the  study 
of  the  filtrate  from  Classes  II  and  III.  Pour  the  liquid 
into  a  small  evaporating-dish,  and  boil  it  gently  for  five  or 
six  minutes  to  expel  the  sulphuretted  hydrogen  with  which 
the  fluid  is  still  charged.  To  make  sure  that  all  the  gas  is 
expelled,  hold  a  bit  of  white  paper  moistened  with  a  solu- 
tion of  acetate  of  lead  (App.,  §  47)  over  the  boiling  liquid; 
when  the  paper  remains  white,  all  the  sulphuretted  hydro- 
gen is  gone.  Next,  add  to  the  liquid  in  the  dish  ten  or 
twelve  drops  of  strong  nitric  acid  (App.,  §  4),  and  again 
gently  boil  the  liquid  for  three  or  four  minutes,  in  order 
that  all  the  iron  present  may  be  converted  into  ferric  salts. 
Then  pour  the  liquid  into  a  test-tube,  add  to  it  about  one 
third  its  bulk  of  chloride  of  ammonium  (App.,  §  20),  and 
finally  add  ammonia- water  (App.,  §  17),  little  by  little,  until 
the  mixture,  after  being  well  shaken,  smells  decidedly  of 
ammonia.  A  brownish-red  precipitate  of  ferric  hydrate  will 
separate  from  the  liquid.  Pour  the  contents  of  the  test-tube 
^on  a  filter,  rinse  the  tube  and  the  precipitate  once  with 
a  little  water,  and  preserve  the  whole  filtrate  for  subsequent 
operations. 

Two  other  metals,  aluminum  and  chromium,  are  precipi- 
tated, as  iron  has  here  been,  by  ammonia-water  under  the 
same  conditions  and  in  the  same  form,  viz.,  as  hydrates. 
These  three  elements,  therefore,  constitute  the  fourth  class, 


§§  9,  10.]  DEFINITION   OF  CLASS  V.  13 

whose  treatment  forms  the  subject  of  Chapter  V.  The 
hydrates  of  these  elements  are  insoluble  in  water,  even  in  the 
presence  of  salts  of  ammonium,  such  as  the  chloride  of  am- 
monium which  has  been  expressly  added,  and  the  nitrate  of 
ammonium  which  has  been  formed  during  the  neutraliza- 
tion of  the  acid  liquid.  The  student  may  be  curious  to 
know  why  the  presence  of  ammonium  salts  is  insisted  upon 
before  the  elements  of  this  class  are  thrown  down  by  am- 
monia-water, j  The  ammonium  salts  have  nothing  to  do 
with  the  precipitation  of  iron,  aluminum  and  chromium; 
but  by  their  presence  they  prevent  the  precipitation,  as  will 
be  hereafter  explained,  of  certain  other  elements  whose 
hydrates,  though  but  slightly  soluble  in  water,  are  dissolved 
by  solutions  of  ammonium  salts.  The  salts  of  ammonium 
are  therefore  added  to  keep  in  solution  certain  other  ele- 
ments which  otherwise  would  encumber  Class  IV.  \ 

10.  Definition  of  Class  V.  —  We  now  proceed  to  the  exami- 
nation of  the  filtrate  from  the  precipitate  of  Class  IV. 
Bring  this  liquid  to  boiling  in  a  test-tube,  and  add  sulphide 
of  ammonium  (App.,  §  18),  little  by  little,  to  the  boiling 
liquid  as  long  as  a  precipitate  continues  to  be  formed.  To 
make  sure  that  the  precipitation  is  complete,  shake  the  hot 
contents  of  the  test-tube  strongly,  and  then  allow  the  mix- 
ture to  settle  until  the  upper  portion  of  the  liquid  becomes 
clear.  Into  this  clear  portion  let  fall  a  drop  of  sulphide  of 
ammonium ;  when  this  drop  produces  no  additional  precipi- 
tate, the  precipitation  is  complete.  Filter  off  the  whitish 
precipitate  of  sulphide  of  zinc,  and  preserve  the  filtrate 
for  further  treatment.  It  sometimes  happens  that  this 
precipitate  refuses  to  settle  and  leave  the  upper  portion  of 
the  liquid  sufficiently  clear  to  test  in  the  manner  described 
above ;  in  this  case  a  small  portion  of  the  mixture  may  be 
filtered  and  a  drop  of  sulphide  of  ammonium  added  to  the 
clear  filtrate  in  order  to  determine  whether  the  precipi- 
tation is  complete.  If  not,  the  filtered  liquid  must  be 
returned  to  the  flask  and  more  of  the  reagent  added. 


14  LETWITION  OF  CLASS  VI  [§§  10,  11. 

I  The  element  zinc,  representing  a  new  class  of  elements, 
is  precipitated  under  the  conditions  of  the  above  experi- 
ment, because  its  sulphide,  though  soluble  in  dilute  acids, 
is  insoluble  in  alkaline  liquids.  |  The  metals  manganese, 
nickel  and  cobalt  resemble  zinc  in  this  respect,  and  these 
four  elements  therefore  form  a  new  class.  Class  V,  in  this 
analytical  method.  The  representative  sulphide  of  this  class 
was  not  precipitated  by  the  sulphuretted  hydrogen  when 
that  reagent  was  employed  to  throw  down  the  members  of 
the  Classes  II  and  III,  because  the  solution  was  at  that  time 
acid.  ;  Again  it  was  not  precipitated  with  Class  IV  by  the 
ammonia-water,  because  the  sulphuretted  hydrogen  with 
which  the  solution  had  previously  been  charged,  was  expelled 
by  boiling  before  the  ammonia-water  was  added. )  The  com- 
plete treatment  of  Class  V  forms  the  subject  of  Chapter  VI. 
11.  Definition  of  Class  VL  — Add  to  the  filtrate  from 
Class  V,  two  or  three  teaspoonfuls  of  carbonate  of  ammo- 
nium (App.,  §  19)  and  boil  the  solution.  A  white  precipitate 
of  carbonate  of  calcium  will  be  produced.  After  boiling, 
allow  the  precipitate  to  settle  until  the  upper  portion  of  the 
liquid  is  comparatively  clear.  To  this  clarified  portion  add 
a  fresh  drop  of  carbonate  of  ammonium.  If  this  drop  pro- 
duce an  additional  precipitate,  more  carbonate  of  ammo- 
nium must  be  added,  and  the  boiling  repeated.  To  the 
partially  clarified  liquid  add  again  a  drop  of  carbonate  of 
ammonium.  This  process  of  making  sure  of  the  complete 
precipitation  of  the  calcium  is  essentially  the  same  as  that 
prescribed  in  precipitating  the  last  class,  and  is,  indeed,  of 
general  application.  When  the  precipitation  of  the  calcium 
has  been  proved  to  be  complete,  filter  the  whole  liquid,  and 
receive  the  filtrate  in  a  small  evaporating-dish.  Calcium  is 
separated  in  the  form  of  carbonate  under  these  circum- 
stances, because  this  carbonate  is  almost  insoluble  in  weak 
alkaline  liquids,  when  an  excess  of  carbonate  of  ammonium 
is   present.      The  allied   elements   barium   and   strontium 


§§  11,  12.]  DEFINITION  OF  CLASS  VII.  15 

behave  in  the  same  way,  so  that  these  three  elements,  viz., 
barium,  strontium  and  calcium,  compose  a  new  class  — 
Class  VI,  whose  complete  treatment  is  set  forth  in  Chapter 
VII. 

12.  Definition  of  Class  VII.  —  Of  the  twenty-four  metallic 
elements,  which  were  to  be  classified  (§  6),  only  three 
remain,  viz.,  magnesium,  sodium  and  potassium.  It  is 
obvious  that  these  three  elements  could  not  have  remained 
in  solution  through  all  the  operations  to  which  the  original 
liquid  has  been  submitted,  unless  their  chlorides  and  sul- 
phides had  been  soluble  in  weak  acids,  and  their  oxides  (or 
hydrates),  sulphides  and  carbonates  soluble  in  dilute  ammo- 
nia-water, at  least  in  presence  of  dilute  solutions  of  ammo- 
nium salts.  It  is  a  fact  that  all  these  compounds  of  sodium 
and  potassium  are  soluble  in  water,  and  in  weak  acid,  alka- 
line and  saline  solutions;  the  magnesium  would  have  been 
partially  precipitated  in  Classes  IV,  V  and  VI,  but  for  the 
presence  of  ammonium  salts  in  the  solution.  These  three 
elements  constitute  Class  VII. 

Evaporate  the  filtrate  from  Class  VI  until  it  is  reduced 
to  one  half  or  one  third  of  its  original  bulk.  Pour  a  small 
part  of  the  evaporated  filtrate  into  a  test-tube ;  add  a  little 
ammonia-water  and  a  teaspoonful  of  phosphate  of  sodium 
(App.,  §  27),  and  shake  the  contents  of  the  tube  violently. 
Sooner  or  later  a  crystalline  precipitate  will  appear.  This 
peculiar  white  precipitate  of  phosphate  of  magnesium  and 
ammonium '  identifies  magnesium ;  but  as  we  have  added  a 
reagent  containing  sodium,  the  filtrate  is  useless  for  further 
examination.  The  liquid  remaining  in  the  evaporating- 
dish  is  then  evaporated  to  dryness,  and  moderately  ignited 
until  fuming  ceases.  All  the  ammoniacal  sal^  which  the 
solution  contained  will  be  driven  off  by  this  means,  and 
there  will  remain  a  fixed  residue,  in  which  are  concentrated 
all  the  salts  of  magnesium  and  sodium  which  the  solution 
contained.    In  this  case  we  have  already  proved  the  presence 


16  SEPARATION  OF  CLASSES.  [§§  12-14. 

of  magnesmm ;  it  remains  to  indicate  briefly  the  nature  of 
the  means  used  to  detect  the  sodium. 

Dissolve  the  residue  in  the  dish,  or  a  portion  of  it,  in 
three  or  four  drops  of  water.  Dip  a  clean  platinum  wire 
(App.,  §  83)  into  this  solution,  and  introduce  this  wire  into 
the  colorless  flame  of  a  gas  or  spirit-lamp  (App.,  §  78). 
An  intense  yellow  coloration  of  the  flame  demonstrates  the 
presence  of  sodium.  A  violet  coloration  would  have  proved 
the  presence  of  potassium.  Magnesium  compounds,  when 
present,  have  no  prejudicial  effect  on  these  characteristic 
colorations.  The  means  of  detecting  each  member  of  this 
last  class  in  presence  of  the  others  will  be  found  described 
in  Chapter  VIII. 

13.  A  condensed  statement  of  the  classification  illustrated 
by  the  foregoing  experiments  is  contained  in  the  table  on 
the  next  page.  All  the  common  metallic  elements  are  em- 
braced in  it.  The  classification  itself  would  not  be  essen- 
tially different,  if  all  the  rare  elements  were  comprehended 
in  it.  The  general  subdivisions  would  be  the  same,  although 
some  of  them  would  embrace  many  more  particulars.       .• 

14.  It  is  essential  to  success  to  follow  precisely  the  pre- 
scribed order  in  applying  the  various  general  reagents.  Class 
I  would  go  down  with  Class  II,  were  hydrochloric  acid  for- 
gotten as  the  first  general  reagent.  Class  II  would  be  pre- 
cipitated in  part  with  Class  IV  and  in  part  with  Class  V  if 
sulphuretted  hydrogen  were  not  used  in  its  proper  place. 
A  large  number  of  the  members  of  the  first 'five  classes 
would  be  precipitated  as  carbonates  with  Class  VI,  were 
they  not  previously  eliminated  by  the  systematic  application 
cf  hydrochloric  acid,  sulphuretted  hydrogen,  ammonia- water 
and  sulphide  of  ammonium  in  the  precise  order  and  under 
the  exact  conditions  above  described.  It  should  be  noticed 
that  all  the  general  reagents  are  volatile  substances,  which 
can  be  completely  removed  by  an  evaporation  to  dryness 
followed  by  a  very  moderate  ignition. 


§14.] 


CLASSIFICATION. 


17 


S,fv 


a  GirtH</j 


jFi  iv*^ 


/i/1/wv*-     yyt^* 


Precipita- 
ted as 
chlorides. 

Ag 
Pb 
Hg 

9 

>■ 

09 
OQ 
M 

Q2SS 

5 

Precipitated  as 
sulphides  insoluble 
in  dilute  acids,  and 
not  redissolved  by 

alkaline  fluids. 

Class  II. 

5&?g& 

Precipitated  as 

sulphides  insoluble 

in  dilute  acids,  but 

redissolved  by 

alkaline  fluids. 

Class  III. 

[together  with  cer- 
tain salts  which  re- 
quire   an   acid  sol- 
vent] . 

Q 

Precipitated  by 

ammonia-water, 

usually  as  hydrates, 

re 

Al 

t 

< 

?si! 

Precipitated 

as  sulphides 

insoluble  in 

alkaline  fluids. 

Zn 

o 

► 

09 
09 

< 

Precipita- 
ted as  car- 
bonates. 

Ca 
Ba 
Br 

a 

>> 

CO 
OB 

< 

«?i 

Remaining 

elements. 

Distinguished 

by  special 

teste. 

o 

< 

H- ( 

O 

It* 
> 

CD 

CO 

CO 

O 
M 

f 


CO 


18  SEPARATION  OF  CLASSES. 

15.  The  series  of  experiments  just  completed  is  merely 
intended  to  demonstrate  the  principles  in  accordance  with 
which  these  twenty-four  elements  are  classified  for  the  pur- 
poses of  qualitative  analysis.  The  general  plan  is  here 
sketched;  the  practical  details,  essential  to  success  in  the 
conduct  of  an  actual  analysis,  will  be  given  hereafter. 


tx 


CHAPTER  II.  ' 

CLASS    I.  — ELEMENTS  WHOSE  CHLORIDES  ARE  INSOLU- 
BLE IN  WATER  AND  ACIDS. 

16.  Example  of  the  Precipitation  of  the  Members  of  Class 
I.  —  Place  in  a  test-tube  five  or  six  drops  of  a  tolerably  con- 
centrated aqueous  solution  of  nitrate  of  silver  (App.,  §  66), 
an  equal  quantity  of  a  solution  of  mercurous  nitrate  and 
two  teaspoonfuls  of  a  solution  of  nitrate  of  lead.  In  case 
the  solution  becomes  turbid  through  the  action  of  carbonic 
acid  dissolved  in  the  water,  pour  in  one  or  two  drops*  of 
nitric  acid  to  destroy  the  cloudiness. 

Add  dilute  hydrochloric  acid  to  the  solution,  drop  by 
drop,  and  shake  the  mixture  thoroughly  after  each  addi- 
tion of  the  acid,  until  the  fresh  portions  of  the  latter  cease 
to  form  any  precipitate  on  coming  in  contact  with  the  com- 
paratively clear  liquor  which  floats  above  the  insoluble 
chlorides.  Finally,  add  three  or  four  more  drops  of  the 
acid  to  insure  the  presence  of  an  excess  of  it  in  the  solu- 
tion. 

17.  Analysis  of  the  Mixed  Chlorides.  —  The  following 
method  of  separating  the  chlorides  of  lead,  silver  and  mer- 
cury, one  from  another,  depends  upon  the  facts :  —  1st. 
That  chloride  of  lead,  though  but  little  soluble  in  cold  water 
or  dilute  hydrochloric  acid,  dissolves  readily  in  boiling 
water,  while  chloride  of  silver  and  subchloride  of  mercury 
(mercurous  chloride,  HgCl)  are  as  good  as  insoluble  in  that 
liquid;  2d.  That  chloride  of  silver  is  soluble  in  ammonia- 
water;  and  3d.  That  mercurous  chloride  is  discolored  by 
ammonia-water  without  dissolving. 

19 


20  SEPARATION   OF  LEAD,  [§  17. 

To  effect  the  separation:  —  Collect  upon  a  filter  the  pre- 
cipitate produced  by  hydrochloric  acid,  allow  it  to  drain,  and 
rinse  it  with  a  few  drops  of  cold  water.  Place  a  clean  test- 
tube  beneath  the  funnel  which  contains  the  filter  and  pre- 
cipitate, thrust  a  glass  rod  through  the  apex  of  the  filter, 
and  wash  the  precipitate  off  the  filter  into  the  test-tube  by 
means  of  a  wash-bottle  which  throws  a  fine  stream. 

Heat  the  mixture  of  water  and  precipitate  to  boiling, 
then  allow  the  precipitate  to  settle  and  pour  off  the  hot 
liquor  upon  a  new  filter,  taking  care  to  retain  the  precipi- 
tate as  far  as  possible  in  the  tube.  To  the  clear  filtrate 
add  two  or  three  teaspoonfuls  of  dilute  sulphuric  acid 
(App.,  §  10).     A  white  cloud  of  sulphate  of  lead  will  be 

Test     formed  in  the  midst  of  the  liquid.     In  case  the 

for      precipitate  contains  a  large  proportion  of  chloride 

^^-  of  lead,  it  may  happen  that  the  hot  water  will  take 
up  so  much  of  it  that  crystals  of  the  chloride  will  separate 
from  the  clear  aqueous  solution  as  it  becomes  cold,  or  that 
the  liquor  will  be  rendered  cloudy  by  the  deposition  of 
numerous  small  particles  of  the  chloride. 

Pour  a  fresh  quantity  of  water  upon  the  precipitate  which 
was  retained  in  the  test-tube,  boil  the  mixture  and,  after 
allowing  the  precipitate  to  subside,  pour  the  nearly  clear 
liquid  upon  the  same  filter  as  before.  This  operation  of 
boiling  the  precipitate  with  successive  portions  of  water  is 
performed  in  order  to  insure  the  complete  removal  of  the 
chloride  of  lead;  the  liquid  is  filtered  through  the  same 
filter  in  order  to  retain  any  particles  of  the  precipitate  which 
fail  to  settle  in  the  tube,  but  it  is  not  necessary  to  save  this 
wash- water  as  most  of  the  chloride  of  lead  was  obtained  in 
the  filtrate  from  the  first  boiling. 

After  the  mixed  precipitate  of  chloride  of  silver  and  mer- 
curous  chloride  has  been  thus  boiled  with  water  several 
times,  cover  it  with  several  teaspoonfuls  of  ammonia-water, 
heat  the  mixture  to  boiling,  and  pour  it  upon  the  filter  used 


§§  17,  18.]  SILVER  AND  MEBCUBT,  21 

in  the  last  paragraph :  the  filtrate  is  to  be  received  in  a  clean 
test-tube.  The  chloride  of  silver,  dissolved  by  the  ammo- 
nia-water, will  pass  into  the  filtrate,  while  the  mercurous 
chloride  suffers  decomposition,  and  is  converted  into  an  ob- 
scure compound  of  mercury,  chlorine,  nitrogen  and  hydrogen, 
which  remains  upon  the  filter  in  the  form  of  an  insoluble 
black  or  gray  powder. 

To  confirm  the  presence  of  silver,  add  to  the  filtrate  dilute 
nitric  acid  (App.,  §  6),  until  the  solution  will  red-      ^est 
den  litmus  paper:  the  chloride  of  silver  is  repre-       for 
cipitated  unchanged  as  soon  as  the  alkaline  solvent     -^S- 
is  neutralized. 

To  confirm  the  presence  of  mercury,  the  metal  itself 
may  be  set  free  by  heating  the  dry  residue  with  carbo- 
nate of  sodium  (App.,  §  25)  in  a  glass  tube.  To  insure 
the  success  of  this  experiment,  wash  into  the  lowest  point 
of  the  filter  the  whole  of  the  black  residue.  As  soon  as 
the  last  drops  of  liquid  have  drained  from  the  filter,  dry 
the  latter,  either  in  a  dish  upon  a  water-bath,  or  J>y  spread- 
ing it  open  upon  a  ring  of  the  iron  stand  (App.,  §  80)  placed 
high  above  a  small  flame  of  the  gas-lamp.  When  the  pre- 
cipitate is  completely  dry,  scrape  it  from  the  paper,  mix  it 
with  an  equal  bulk  of  carbonate  of  sodium  pre-  ^est 
viously  dried  over  the  gas-lamp  on  platinum  foil  for 
(App.,  §  83)  unless  already  perfectly  dry,  and  trans-  ^6- 
fer  the  mixture  to  the  bottom  of  a  glass  tube.  No.  5  (App., 
§  86),  closed  at  one  end.  Then  wipe  out  the  inside  of  the 
tube  with  a  tuft  of  cotton  fixed  to  a  wire,  or  with  a  twisted 
slip  of  paper,  and  heat  the  closed  end  of  the  tube  for  two 
or  three  minutes  in  the  flame  of  a  gas-lamp.  A  sublimate 
of  finely  divided  metallic  mercury  will  form  upon  the  walls 
of  the  tube ;  it  will  cohere  to  visible  globules  when  scratched 
with  a  piece  of  iron  wire. 

18.  An  outline  of  the  operations  described  in  the  fore- 
going paragraphs  may  be  presented  in  tabular  form,  as  fol- 
lows :  — 


22  CLASS  I.  [§§  18,  19. 


The  General  Reagent  (HCl)  of  Class  I  precipitates  PbClj,  AgCl 
and  HgCl.     When  the  precipitate  is  boiled  with  water :  — 


PbCla  goes  into 
solution.  C  o  n  - 
firm  presence  of 
lead  by  precipita- 
tion of  sulphate 
of  lead. 


AgCl   and  HgCl  remain '  undissolved.     On 
treating  the  mixture  with  ammonia- water :  — 


AgCl  dissolves. 

Confirm  presence 
of  silver  with  nitric 
acid. 


A  black  compound  of 
Hg  remains  undissolved. 
Confirm  presence  of  Hg 
by  isolating  the  metal. 


19.  In  the  actual  analysis  of  a  solution  of  unknown  com- 
position, a  precipitate  might  under  certain  circumstances 
be  formed  on  the  addition  of  hydrochloric  acid,  even  in  the 
absence  of  all  members  of  Class  I.  This  might  occur  in 
case  the  liquid  under  examination  contained  a  hyposulphite 
(thiosulphate) ;  for  this  class  of  salts  is  decomposed,  with 
evolution  of  sulphurous  acid  and  deposition  of  sulphur, 
on  the  addition  of  the  general  reagent  (HCl)  of  Class  I. 
Some  sulphides  also  are  decomposed  by  hydrochloric  acid, 
with  deposition  of  sulphur.  An  acid  solution  of  antimony, 
bismuth  or  tin  with  some  acid  other  than  hydrochloric 
may  give  a  precipitate  of  the  basic  chlorides  of  these  ele- 
ments: their  basic  chlorides  are  soluble  in  an  excess  of 
hydrochloric  acid.  Concentrated  solutions  of  certain  salts 
such  as  barium  chloride  and  nitrate,  sodium  chloride,  etc., 
may  give  a  precipitate  of  the  salt  itself,  on  the  addition  of 
hydrochloric  acid;  such  precipitates  are  readily  soluble  in  a 
small  amount  of  water.  A  gelatinous  white  precipitate  of 
hydrated  silicic  acid  might  also  be  formed  at  this  stage, 
and  other  precipitates  in  certain  circumstances,  as  will  be 
explained  het.eafter  (§§  70  and  88,  I.  C). 


CHAPTER  III. 

CLASS  II.  — ELEMENTS  WHOSE  SULPHIDES  ARE  INSOLU^ 
BLE  IN  WATER,  DILUTE  ACIDS  AND  ALKALIES. 

20.  Example  of  the  Precipitation  of  the  Members  of  Class 
n.  —  Place  in  a  small  beaker  a  half  teaspoonful  of  a  solution 
of  each  of  the  following  substances:  —  mercuric jchlori^e 
(corrosive  sublimate),  chloride  of  bismuth,  of  cadmiuin  and 
of  copper,  together  with  two  or  three  teaspoonfuls  of  a  cold 
aqueouT  solution  of  chloride  of  lead.  Pill  the  beaker  half 
full  of  water :  a  white  precipitate  of  the  basic  chloride  of 
bismuth  usually  falls  on  the  addition  of  the  water,  which 
may  be  disregarded. 

Heat  the  liquid  in  the  beaker  nearly  or  quite  to  boiling, 
then  place  the  beaker  beneath  a  chimney  or  in  a  strong 
draught  of  air,  and  saturate  the  solution  with  sulphuretted 
hydrogen  gas.  To  determine  when  enough  sulphuretted 
hydrogen  has  been  passed  through  the  liquid,  remove  the 
beaker  every  four  on  five  minutes  from  the  source  of  the 
gas,  blow  away  the  gas  which  lies  in  the  beaker  above 
the  liquid,  and  stir  the  latter  thoroughly  with  a  glass  rod. 
If,  after  the  lapse  of  two  or  three  minutes,  the  liquid  still 
smells  strongly  of  sulphuretted  hydrogen,  it  is  saturated 
with  the  gas  and  ready  to  be  filtered.  But  in  case  no  per- 
sistent odor  of  sulphuretted  hydrogen  is  observed,  the  gas 
must  be  passed  anew  through  the  liquor  until  it  has  become 
fully  saturated.  Since  some  of  the  substances  above  enu- 
merated are  thrown  down  more  quickly  by  sulphuretted 
hydrogen  than  the  others,  it  is  absolutely  necessary  to  em- 
ploy the  reagent  in  excess  in  order  that  those  members  of 

23 


24  SEPARATION   OF  CLASS  II.  [§§  29)  21. 

the  class  which  are  least  easily  precipitated  may  not  escape 
detection.  To  make  sure  that  precipitation  is  complete 
filter  a  portion,  and  to  the  clear  filtrate  in  a  test-tube  or 
small  beaker  add  an  equal  volume  of  sulphuretted  hydrogen 
water;  if  any  precipitate  appear,  the  whole  of  the  liquid 
should  be  diluted,  and  sulphuretted  hydrogen  passed  through 
it  again  until  a  portion  filtered  and  tested  as  before  gives 
no  precipitate.  If  the  solution  is  too  strongly  acid,  there  is 
great  danger  of  incomplete  precipitation,  especially  of  cad- 
mium. 

21.  Analysis  of  the  Mixed  Sulphides.  —  The  following 
method  of  separating  the  members  of  Class  II  depends 
upon  the  facts :  —  1st.  That  mercuric  sulphide  is  insoluble 
in  hot  dilute  nitric  acid,  while  the  other  sulphides  are  con- 
verted thereby  into  soluble  nitrates.  2d.  That  sulphate  of 
lead  is  insoluble  in  acidulated  water,  while  the  sulphates 
of  the  other  -djiembers  of  the  class  are  soluble.  3d.  That 
hydrate  of  bismuth  is  insoluble  in  ammonia-water,  while 
the  hydrates  of  cadmium  and  copper  are  soluble  in  that 
liquid.  4th.  That  sulphide  of  copper  is  soluble  in  solution 
of  cyanide  of  potassium  while  sulphide  of  cadmium  is 
insoluble. 

To  effect  the  separation :  —  Collect  the  precipitated  sul- 
phides upon  a  filter;  wash  the  precipitate  thoroughly  with 
successive  portions  of  water  until  the  wash-water  is  no 
longer  acid  to  litmus  paper;  transfer  the  precipitate  to  a 
small  parcel^in  dish,  pour  upon  it  four  or  five  times  as 
much  dilute  nitric  acid  as  would  be  sufiicient  to  cover  it, 
and  boil  the  mixture  during  two  or  three  minutes,  stirring 
it  constantly  with  a  glass  rod,  and  adding  water  or  dilute 
nitric  acid  at  intervals  to  replace  the  liquid  which  evapo- 
rates. All  the  sulphides  with  the  exception  of  the  sulphide 
of  mercury  are  decomposed  and  the  several  elements  go  into 
solution  as  nitrates ;  the  sulphide  of  mercury,  mixed  with 
some  free  sulphur  resulting  from  the  decomposition  of  the 


§  21.]  SEPARATION  OF  MERCURY.  25 

other  sulphides,  remains  undissolved  as  a  heavy  dark-colored 
mass.  Decant  the  nitric  acid  solution  into  a  filter,  collect 
the  filtrate  in  a  second  porcelain  dish,  and  evaporate  it 
nearly  to  dryness  in  order  to  drive  off  the  greater  part  of 
the  free  nitric  acid  before  examining  it  for  the  elements 
supposed  to  be  contained  in  it. 

The  residue  containing  mercury,  insoluble  in  dilute  nitric 
acid,  may  sometimes  be  light  colored  if  the  boiling  with 
nitric  acid  is  too  prolonged,  or  if  a  trace  of  hydrochloric  acid 
is  present.  Hence  any  residue  remaining  after  the  treat- 
ment with  nitric  acid,  unless  it  is  evidently  sulphur,  should 
be  examined. 

The  residue  insoluble  in  nitric  acid  which  was  left  in  the 
first  dish,  is  to  be  washed  with  water  in  order  to  remove 
the  adhering  solution.  This  may  generally  be  done  by  pour- 
ing water  into  the  dish,  allowing  the  precipitate  to  settle 
and  then  decanting  the  wash- water;  it  is  sometimes  neces- 
sary, however,  to  collect  the  precipitate  on  a  filter  and  wash 
in  the  ordinary  manner.  In  either  case  the  wash-water  is 
thrown  away  and  the  precipitate  is  boiled  in  the  porcelain 
dish  with  as  much  aqua  regia  (App.,  §  7)  as  will  barely 
cover  it.  Dilute  the  acid  solution  obtained  with  an  equal 
volume  of  water,  remove  from  it,  by  filtration  or  other- 
wise, any  particles  of  free  sulphur  which  may  remain 
undissolved,  and  add  to  it  almost,  but  not  quite,  enough 
ammonia- water  to  neutralize  its  acidity.  In  case  of  the 
accidental  addition  of  too  much  ammonia-water,  manifested 
by  the  appearance  of  a  precipitate  and  by  the  alkaline 
reaction  on  litmus,  the  solution  must  be  made  just  acid  by 
the  cautious  addition  of  nitric  acid,  a  drop  at  a  time.  Place 
in  the  slightly  acid  solution  a  small  bit  of  bright  -pest 
copper  wire,  and  observe  that  metallic  mercury  is  for 
deposited  upon  the  copper  as  a  white  silvery  ^S- 
coating.  After  the  lapse  of  ten  or  fifteen  minutes,  dry  the 
wire  upon  blotting  paper,  drop  it  into  a  narrow  glass  tube 


26  SEPARATION  OF  BISMUTH.  [§  21. 

which  has  been  sealed  at  one  end,  and  heat  it  at  the  lamp. 
Metallic  mercury  will  sublime,  and  be  deposited  as  a  dull 
mirror  upon  the  cold  portions  of  the  glass.  By  scratching 
the  sublimate  with  the  point  of  a  bit  of  iron  wire,  the  metal 
may  be  made  to  collect  into  visible  globules. 

When  the  greater  part  of  the  free  nitric  acid  has,  by  the 

aforesaid   evaporation,  been   driven  off   from   the  filtrate 

which  contains  the  mixed  nitrates  of  lead,  bismuth,  cadmium 

Test     ^i^cl  copper,  transfer  the  residual  liquor  to  a  test- 

for      tube,  mix  it  with  two  or  three  times  its  volume  of 

^^-      dilute  sulphuric  acid,  add  half  its  own  volume  of 

alcohol,   and  leave  the  mixture  at  rest  during  fifteen  or 

twenty  minutes.     Sulphate  of  lead  will  be  thrown  down  as 

a  white  powder,  plainly  to  be  seen  in  the  test-tube,  though 

it  would  have  been  scarcely  visible  in  the  white  dish. 

Collect  the  filtrate  from  the  sulphate  of  lead  in  a  small 
beaker,  and  add  to  it  ammonia-water  by  repeated  small 
portions,  'taking  care  to  stir  the  liquid  thoroughly  after 
each  addition  of  the  ammonia,  until  a  strong,  persistent 
odor  of  the  latter  is  perceptible.  The  hydrates  of  copper, 
cadmium  and  bismuth  will  all  be  thrown  down  at  first, 
but  the  hydrates  of  copper  and  cadmium  will  redissolve  in 
the  excess  of  ammonia-water,  and  hydrate  of  bismuth  will 
alone  be  left  as  an  insoluble  precipitate.  The  blue  color  of 
the  solution  is  due  to  the  presence  of  copper.  If  in  the  case 
of  the  actual  examination  of  a  solution  of  unknown  com- 
position no  precipitate  falls  on  the  addition  of  the  ammo- 
nia-water, this  does  not  prove  the  absence  of  copper  and 
cadmium,  as  the  hydrates  may  be  dissolved  by  the  ammo- 
nia-water as  fast  as  formed,  and  thus  escape  observation. 

To  prove  that  the  precipitate  contains  bismuth :  —  Collect 

Test      it  upon  a  filter,  allow  it  to  drain,  and  dissolve  it 

for       in  the  smallest  possible  quantity  of  strong  hydro- 

^*-      chloric  acid  poured  drop  by  drop  upon  the  sides 

of  the  filter;  carefully  evaporate  the  acid  solution  to  the 


§  21.]  SEPARATION  OF  CADMIUM.  27 

bulk  of  two  or  three  drops,  and  pour  it  into  a  large  test- 
tube  nearly  full  of  water.  A  dense,  milky  cloud  of  insol- 
uble basic  chloride  of  bismuth  will  appear  in  the  water. 
Since  sulphate  of  lead  is  not  absolutely  insoluble  in  water 
which  contains  nitric  acid,  a  slight  precipitate  of  hydrate 
of  lead  might  be  produced  on  the  addition  of  the  ammonia- 
water  even  when  no  bismuth  was  present  in  the  solution. 
To  prove  the  presence  of  bismuth,  the  oxychloride  must 
always"  be  <?arefully  tested  for.  It  is  to  be  remarked  that  if 
the  amount  of  hydrate  of  bismuth  is  in  any  case  small,  con- 
siderable jiare  must  be  exercised  in  applying  the  confirma- 
tory test.  In  such  a  case  the  basic  chloride  may  appear 
as  white  threads  marking  the  path  of  the  heavier  liquid 
through  the  water,  and  gradually  producing  more  or  less 
turbidity  throughout  the  whole  mass  of  the  water. 

The  blue  color  of  the  ammoniacal  filtrate  from  the  hydrate 
of  bismuth  indicates  the  presence  of  copper,  and  when  well 
defined  is  of  itself  a  sufficient  proof  of  the  presence  of 
this  element.  But  in  the  absence  of  a  marked  blue  colora- 
tion, at  this  stage,  copper  should  be  specially  tested  for  in 
the  manner  described  below. 

To  prove  the  presence  of  copper  and  cadmium,  proceed  as 
follows :  —  Divide  the  ammoniacal  filtrate  into  two  portions. 

To  prove  the  presence  of  copper  in  case  no  blue  colora- 
tion has  appeared :  —  Concentrate  one  portion  in  an  evapo- 
rating-dish,  acidify  with  acetic  acid  (App.,  §  13),      Test 
transfer  to  a  test-tube,  and  add  one  or  two  drops  of      for 
a  solution  of  ferrocyanide  of  potassium  (App.,  §  34).      ^^• 
A  peculiar  reddish-brown  precipitate  of  ferrocyanide  of  cop- 
per will  fall  in  case  much  copper  is  present,  and  even  when 
the  proportion  of  copper  in  the  solution  is  extremely  small 
a  light  brownish-red  cloudiness  will  be  produced. 

To  prove  the  presence  of  cadmium :  —  Add  cyanide  of 
potassium  solution  (App.,  §  36)  to  the  other  portion  of 
the  alM.ine  filtrate  (if  blue  coloration  showing  the  pres- 


28  SEPARATION  OF  CADMIUM.  [§§^1,22. 

ence  of  copper  has  been  visible,  the  whole  of  the  alkaline 
filtrate  may  be  used)  until  decolorized;  if  no  blue  color 
has  appeared,  only  a  few  drops  of  the  cyanide  of  potassium 
Test  solution  need  be  added;  pass  sulphuretted  hydro- 
for  gen  through  the  solution,  or  add  sulphuretted 
^^-  hydrogen  water.  The  liquid  immediately  be- 
comes cloudy  from  the  presence  of  minute  particles  of 
sulphide  of  cadmium  of  characteristic  yellow  color.  In 
case  an  exceedingly  small  amount  of  cadmium  iT'present 
there  may  be  only  a  yellow  coloration:  the  sulphide  can 
even  in  this  case  be  rendered  visible  by  fillRffion,  the 
yellow  precipitate  remaining  on  the  filter.  If  on  passing 
sulphuretted  hydrogen  through  the  solution  a  black  or  dark- 
colored  precipitate  is  obtained,  it  may  be  due  to  the  pres- 
ence of  lead  or  mercury  —  in  the  former  case  because  the 
lead  was  not  completely  removed  as  sulphate,  in  the  latter 
case  because  the  element  was  not  completely  converted  into 
the  black  sulphide.  In  case  other  than  a  yellow  precipitate 
appears,  filter  and  wash  the  precipitate,  boil  it  in  an  evapo- 
rating-dish  with  dilute  sulphuric  acid  (App.,  §  11),  filter 
again  and  pass  sulphuretted  hydrogen  through  the  filtrate; 
but  if  the  precipitate  is  still  black,  owing  to  the  presence  of 
sulphide  of  mercury,  it  must  be  boiled  with  concentrated 
hydrochloric  acid,  which  will  dissolve  the  sulphide  of 
cadmium  if  present:  the  solution  is  then  largely  diluted 
with  water  and  again  tested  with  sulphuretted  hydrogen. 

22.   The  operations  above  described  may  be  presented  in 
tabular  form  as  follows :  — 


f§  22,  23.]      SEPARATION  OF  CLASSES  I  AND  II. 


29 


The  General  Keagent  (H^S)  of  Class  II  precipitates  HgS,  PbS, 
Bi^Sa,  CdS  and  CuS  (as  well  as  members  of  Class  III,  which 
are  subsequently  separated  by  solution  in  sulphide  of  sodium). 
The  precipitate  is  boiled  with  dilute  nitric  acid :  — 


A  residue  of 
HgS,  mixed 
with  S,  re- 
mains. 

Confirm 
presence  of 
Hg  with  cop- 
per w^e. 


,Pb,  Bi,  Cd  and  Cu  go  into  solution  as  nitrates. 
On  addhig  dilute  sulphuric  acid  and  half  its  volume 
of  alcohol  to  the  concentrated  solution  :  — 


PbSO^    i  s 
thrown  down. 


The  sulphates  of  Bi,  Cd  and  Cu 

remain  in  solution.    On  adding  an  ex- 
cess of  ammonia- water :  — 


Hydrate  of 
Bismuth  is 
thrown  down. 
Confirm  Bi 
by  precipitat- 
ing the  oxy- 
chloride. 


'  Compounds  of  Cd 
and  of  Cu  remain  in 
solution. 


Divide  into  two  por- 
tions. A  and  B. 


A.  Acid- 
ify  with 
acetic  acid. 
Confirm 
presence 
of  copper 
by  testing 
with  f erro- 
cyanide  of 
potassium. 


B.  Add 

cyanide  of 
potassium. 
Confirm 
presence 
of  cadmi- 
um by  pre- 
cipitation 
of  CdS. 


23.  The  Method  of  Separating  Class  I  from  Class  II  has 
already  been  x^articularly  described  in  §  6.  It  should  be 
observed,  however,  that  even  if  no  member  of  Class  I  were 
present  in  the  mixture  to  be  analyzed,  it  would  still  be 
necessary  to  acidulate  the  liquid  with  hydrochloric  acid, 
before  passing  the  sulphuretted  hydrogen,  in  order  to 
prevent  the  precipitation  of  members  of  Classes  IV  and  V, 
and  to  secure  the  complete  precipitation  of  members  of 
Class  III. 

The  liquid  should  be  watched  attentively  when  the 
stream  of  sulphuretted  hydrogen  first  begins  to  flow  through 
it,  since  useful  inferences  may  often  be  drawn  from  the 
various  phenomena  which  present  themselves. 


30  SEPARATION   OF  CLASSES  II  AND  III,       [§  23. 

a.  Tims,  the  formation  of  a  white  precipitate  which 
afterwards  changes  to  yellow,  orange,  brownish-red,  and 
finally  to  black,  as  the  liquid  gradually  becomes  saturated 
with  the  gas,  indicates  the  presence  of  mercuric  chloride. 
In  order  to  exhibit  this  reaction,  pass  sulphuretted  hydrogen 
through  two  or  three  teaspoonfuls  of  a  solution  of  mercuric 
chloride.  The  white  precipitate  at  first  formed  is  a  com- 
pound of  chloride  and  sulphide  of  mercury,  but  by  the  action 
of  successive  portions  of  sulphuretted  hydrogen  the  com- 
position and  appearance  of  the  precipitate  is  changed,  until 
it  has  been  completely  converted  into  black  sulphide  of 
mercury.  It  is  important  that  the  mercury  should  be  com- 
pletely converted  into  sulphide,  as  the  compound  just  men- 
tioned is  soluble  in  nitric  acid :  the  result  is  rendered  more 
certain  if  the  solution  be  warmed  before  being  treated  with 
sulphuretted  hydrogen. 

b.  If  the  precipitate  is  of  a  dull  red  color  at  first,  after- 
wards changing  to  black,  the  probable  presence  of  lead  is 
indicated;  for  sulphuretted  hydrogen  throws  down  from 
solutions  which  contain  much  free  hydrochloric  acid  a  red 
compound  of  chloride  of  lead  and  sulphide  of  lead,  which  is 
afterwards  decomposed,  with  formation  of  the  black  sul- 
phide, when  the  solution  becomes  saturated  with  the  gas. 

c.  A  decided  bright  yellow  precipitate  would  indicate  the 
presence  of  cadmium,  arsenic  or  tin;  of  these  three,  cadmium 
is  distinguished  by  the  fact  that  its  sulphide  remains 
undissolved  when  the  precipitate  is  treated  with  sulphide 
of  sodium  to  separate  the  members  of  Class  III. 

But  even  from  solutions  which  contain  no  members  of 
Classes  II  or  III,  yellow-white  or  milky-white  precipitates 
of  free  sulphur  are  often  thrown  down;  for  sulphuretted 
hydrogen  is  easily  decomposed,  with  deposition  of  sulphur, 
by  a  variety  of  oxidizing  agents,  such  as  nitric,  chromic 
and  chloric  acids,  and  solutions  of  ferric  salts  and  of  free 
chlorine.  If  the  solution  under  examination  contained 
much  nitric  acid,  sulphuretted  hydrogen  would  have  to  be 


§  23.]       SEPARATION  OF  CLASSES  II  AND  III.  31 

passed  through  it  for  a  long  time  to  destroy  the  acid,  before 
the  liquid  could  be  saturated  with  the  gas.  •  In  this  case 
the  sulphur  separates  as  a  tenacious  mass  of  dirty  yellow 
color;  but  in  most  instances,  notably  when  the  solution 
contains  a  ferric  salt,  the  sulphur  is  precipitated  in  the 
form  of  exceedingly  minute  particles,  which  impart  to  the 
solution  a  peculiar  milkiness  or  opalescence.  These  parti- 
cles are  so  fine  that  they  pass  through  the  pores  of  filter 
paper ;  they  cannot  be  removed  by  filtration.  To  see  this 
separation  of  sulphur,  pass  sulphuretted  hydrogen  through 
two  or  three  teaspoonfuls  of  a  solution  of  ferric  chloride; 
also  through  nitric  acid  diluted  with  an  equal  volume  of 
water. 

If  the  original  solution  contains  a  chromate,  its  yellow  or 
reddish-yellow  color  will  be  changed  to  green  by  the  action 
of  sulphuretted  hydrogen;  for  the  chromate  is  reduced  to 
the  condition  of  chromic  chloride :  — 

2  MjCrO^  +  10  HCl  +  3  HjS  =  2  CrClj  +  3  S  +  4  MCI  +  8  HjO. 

To  show  this  reduction,  pass  sulphuretted  hydrogen 
through  two  or  three  teaspoonfuls  of  a  solution  of  chromate 
of  potassium  to  which  a  few  drops  of  hydrochloric  acid  have 
been  added. 

The  sulphur  is  set  free  in  the  form  of  the  minute  white 
particles  above  described,  and  remains  suspended  in  the 
green  liquid,  looking  not  unlike  a  green  precipitate. 

d.  The  immediate  formation  of  a  black  precipitate  in- 
dicates the  presence  of  copper  or  bismuth,  and  it  is  to  be 
observed  that  either  of  these  black  precipitates  would  ob- 
scure the  colors  of  the  other  sulphides  of  the  class,  and 
conceal  them  if  present. 

e.  If  no  precipitate  appears  even  when  the  liquid  has 
become  saturated  with  the  gas,  or  only  a  slight  cloudiness 
from  the  decomposition  of  the  sulphuretted  hydrogen,  the 
absence  of  every  member  of  Classes  II  and  III  is,  of  course, 
to  be  inferred. 


CHAPTER  IV. 

CLASS  III.  —  ELEMENTS  WHOSE  SULPHIDES  ARE  INSOL- 
UBLE IN  WATER  OR  DILUTE  ACIDS,  BUT  SOLUBLE  IN 
ALKALINE  SOLUTIONS. 

24.  Example  of  the  Precipitation  of  the  Members  of  Class 
III.  —  Place  in  a  small  beaker  six  or  eight  drops  of  a  solu- 
tion of  arsenious  oxide  in  hydrochloric  acid  and  similar 
quantities  of  solutions  of  the  chlorides  of  antimony  and  tin. 
Pour  in  enough  dilute  hydrochloric  acid  to  half  fill  the 
beaker ;  a  white  precipitate  of  the  basic  chloride  of  antimony 
may  form,  which  can  be  disregarded. 

Pass  sulphuretted  hydrogen  gas  through  the  solution,  in 
the  manner  described  in  §  20,  until  the  odor  of  the  gas 
persists.  Then  collect  the  precipitated  sulphides  upon  a 
filter,  and  rinse  the  precipitate  once  or  twice  with  water. 

In  the  analysis  of  any  complex  solution  of  unknown  com- 
position which  might  contain  one  or  all  of  the  members  of 
Class  III,  the  sulphides  of  this  class  would,  of  course,  all  be 
thrown  down  at  the  same  time  as  those  of  Class  II.  (Com- 
pare §§  8,  22.)  It  will  be  well,  therefore,  for  the  sake  of 
illustration,  for  the  student  to  dissolve  the  present  precip- 
itate in  sulphide  of  sodium  in  order  that  he  may  begin  the 
treatment  of  Class  III  at  the  precise  point  at  which  this 
class  would  be  encountered  in  an  actual  analysis ;  namely, 
with  the  sulphides  of  the  class  in  alkaline  solution.  To 
this  end,  allow  the  washed  precipitate  to  drain,  spread  out 
the  filter  upon  a  plate  of  glass,  scrape  the  precipitate  from 
the  paper  with  a  small  spatula  of  platinum,  horn  or  wood, 
and  transfer  it  to  a  porcelain  dish.  Pour  lipou  the  precipi- 
32 


§§  24,  25.]  SEPARATION  OF  CLASS  III.  33 

tate  two  or  three  times  as  much  of  a  solution  of  sulphide  of 
sodium  as  would  be  sufficient  to  cover  it,  and  boil  the  mix- 
ture very  cautiously,  so  as  to  avoid  spattering.  The  pre- 
cipitate will  soon  dissolve,  and  no  solid  matter  will  be  left 
suspended  in  the  solution,  excepting  a  few  fibres  of  the 
filter  paper.  If  nearly  complete  solution  does  not  ensue, 
the  undissolved  portion  is  probably  SnS;  in  which  Q3.se 
allow  the  undissolved  substance  to  settle,  decant  off  the 
liquid  and  to  the  precipitate  add  a  little  of  the  yellow  sul- 
phide of  sodium  solution  and  warm,  or  a  pinch  of  flowers 
of  sulphur  may  be  added  to  the  boiling  sulphide  solution. 
When  solution  has  taken  place  mix  this  liquid  with  that 
just  decanted  and  proceed.  In  the  case  of  an  actual  analy- 
sis when  sulphides  of  members  of  Class  II  are  present,  the 
yellow  sulphide  should  always  thus  be  finally  employed 
(or  a  little  sulphur  added  as  above),  an  excess  being,  how- 
ever, avoided.  It  is  such  a  solution  as  this  which  in  an 
actual  analysis  is  examined  for  members  of  Class  III  by 
either  of  the  following  methods.  Divide  the  solution 
obtained  into  two  portions,  using  one  portion  for  the  first .^j  ^ 
method  of  analysis :  the  other  for  the  second  method.  JjHB 

25.  Analysis  of  the  Mixed  Sulphides.  —  First  methoo^^^ 
This  method  depends,  1st.  Upon  the  oxidation  of  the 
several  sulphides  by  means  of  nitric  acid  and  nitrate  of 
sodium,  and  the  conversion  of  arsenic  into  a  compound 
soluble  in  water,  while  antimony  and  tin  are  converted  into 
insoluble  compounds ;  2d.  Upon  the  fact  that  the  tin  in  the 
compound  thus  formed  is  set  free  in  the  metallic  state  when 
this  compound  is  treated  with  zinc  and  hydrochloric  acid, 
while  the  antimony  under  similar  circumstances  is  in  part 
reduced  to  metallic  antimony  and  in  part  conv^ed  into 
antimoniuretted  hydrogen;  3d.  Upon  the  solubility  of  tin 
and  insolubility  of  gold  and  platinum  in  strong  hydrochloric 
acid. 
:    To  effect  the -separation  I: — Add  strong  nitric  acid  to  the 


34  SEPABATION  OF  ARSENIC.  [§  25. 

sulphide  of  sodium  solution  until  the  reaction  is  distinctly- 
acid;  a  precipitate  forms  which  consists  partly  of  the  sul- 
phides of  arsenic,  antimony  and  tin,  and  partly  of  sulphur 
from  the  decomposition  of  the  alkaline  sulphide.  Without 
heeding  the  precipitate  which  separates,  evaporate  the  acid 
mixture  to  the  bulk  of  half  a  teaspoonfulj  then  add  solid 
carbonate  of  sodium  ve^y  cautiously  until  the  last  addition 
causes  no  further  effervescence.  Then  add  about  half  a 
teaspoonful  of  a  mixture  of  equal  parts  of  solid  carbonate 
and  nitrate  of  sodium.  Heat  the  mass  with  constant  stir- 
ring until  it  fuses.  The  fused  mass  should  be  white  (if  no 
gold  or  platinum  are  present  as  in  this  case)  and  liquid.  It 
is  sometimes  necessary  to  add  more  of  the  mixture  of  nitrate 
and  carbonate  of  sodium  towards  the  latter  part  of  the 
fusion,  especially  if  too  great  an  excess  of  the  alkaline 
sulphide  has  been  used  in  making  the  solution.  Pour  out 
the  liquid  mass,  as  far  as  may  be  possible,  upon  a  bit  of 
cold  porcelain,  and  when  it  has  cooled  somewhat,  transfer 
it,  together  with  whatever  can  be  detached  from  th%  dish  in 
which  the  fusion  was  made,  to  a  clean  mortar  and  reduce  it 
to  powder.  Eeturn  this  powder  to  the  porcelain  dish,  and 
when  the  dish  with  its  contents  is  perfectly  cold  pour  in 
several  teaspoonfuls  of  cold  water  and  allow  the  mixture 
to  stand,  stirring  it  from  time  to  time,  until  that  portion  of 
the  fused  mass  which  could  not  be  detached  from  the  dish 
has  softened  and  is  in  part  dissolved;  finally,  filter  the 
solution.  By  the  treatment  with  nitric  acid  and  nitrate  of 
sodium  the  arsenic  of  the  sulphide  of  arsenic  has  been  con- 
verted into  arseniate  of  sodium,  a  compound  which  is  solu- 
ble in  water  and  which  passes  into  the  filtrate  together  with 
the  excess  of  nitrate  and  carbonate  of  sodium  and  some 
sulphate  of  sodium  formed  during  the  process.  The  anti- 
mony has  been  converted  into  antimoniate  of  sodium  and 
the  tin  into  the  binoxide;  these  two  compounds,  being 
scarcely  at  all  soluble  in  water,  remain  on  the  filter.    (Gold 


§  26.]  SEPARATION  OF  ARSENIC.  35 

and  platinum  if  present  in  the  original  solution  will  here 
be  in  the  metallic  condition.)  This  insoluble  residue  is 
examined  for  antimony  and  tin  in  a  manner  presently  to  be 
described. 

To  the  filtrate  add  nitric  acid  drop  by  drop  until  the 
liquid  shows  a  faintly  acid  reaction;  warm  gently  to  remove 
all  traces  of  carbonic  acid  set  free  by  the  action  of  the  nitric 
acid  on  the  excess  of  carbonate  of  sodium  used  in  the  fusion. 
If  a  precipitate  appears  on  addition  of  nitric  acid,  it  is 
probably  a  hydrate  of  tin,  and  its  appearance  is  due  to  the 
fact  that  the  fusion  with  nitrate  of  sodium  was  carried  on 
at  so  high  a  temperature  that  a  portion  of  the  nitrate  of 
sodium  was  converted  into  oxide  of  sodium,  and  this  acting 
on  the  oxide  of  tin  formed  a  certain  amount  of  soluble 
stannate  of  sodium.  The  precipitate,  if  any  appear,  should 
be  filtered  off  and  added  to  the  insoluble  residue  xest 
which  awaits  examination.  To  one  half  of  the  for 
clear  filtrate  add  ammonia-water  to  alkaline  reac-  "^^• 
tion,  then  a  few  drops  of  a  prepared  solution  of  chloride  of 
magnesium  and  chloride  of  ammonium  (App.,  §  48)  and 
set  the  mixture  aside  for  twelve  hours.  The  formation  of 
a  white  crystalline  precipitate  of  arseniate  of  ammonium  and 
magnesium  is  evidence  of  the  presence  of  arsenic. 

To  the  remainder  of  the  filtrate  which  contains  the  arsenic, 
and  which  should  contain  the  smallest  possible  quantity  of 
free  nitric  acid,  add  a  small  quantity  of  a  solution  of  nitrate 
of  silver.  On  the  addition  of  nitrate  of  silver  a  precipitate 
generally  falls  even  in  the  absence  of  arsenic,  owing  to  the 
fact  that  the  nitrate  of  sodium  used  in  the  fusion  usually 
contains  some  chloride  of  sodium,  and  in  order  that  the 
arsenic  present  may  be  converted  into  arseniate  of  silver  a 
small  quantity  of  nitrate  of  silver  must  be  added  over  and 
above  that  necessary  to  remove  the  chlorine  present.  The  pre- 
cipitated chloride  of  silver  is  removed  by  filtration.  To 
the  clear  filtrate  add  a  solution  of  pure  acetate  of  sodium 


36  SEPARATION   OF  ANTIMONY.  [§25. 

(App.,  §  28)  drop  by  drop,  mixing  thoroughly  after  each  ad- 
dition, until  the  mixture  smells  of  acetic  acid;  a  red  or 
brownish-red  precipitate  of  arseniate  of  silver  appears. 
The  acetate  of  sodium  is  added  because  the  arseniate  of 
silver  is  soluble  in  nitric  acid,  and  but  sparingly  soluble  in 
acetic  acid  unless  it  is  present  in  considerable  excess.  On 
the  addition  of  acetate  of  sodium  to  the  liquid  containing 
free  nitric  acid  there  was  formed  nitrate  of  sodium,  and 
acetic  acid  was  set  free.  That  the  test  be  satisfactory,  the 
following  precautions  must  be  carefully  observed.  The 
filtrate  from  the  fusion  must  be  distinctly  acid  with  nitric 
acid  and  free  from  all  traces  of  carbonic  acid,  but  must  not 
contain  a  great  excess  of  the  acid.  Care  must  be  taken  that 
enough  nitrate  of  silver  is  added  and  that  the  solution  of 
acetate  of  sodium  contains  no  organic  matter,  which  often 
appears  in  solutions  of  this  reagent  which  have  been  kept 
for  some  time. 

Any  precipitate  supposed  to  contain  arsenic  (if  in  the 
form  of  sulphide,  it  must  be  converted  into  some  other  com- 
pound) may  be  further  examined  by  converting  the  arsenic 
into  a  hydrogen  compound  by  the  method  known  as  "  Marsh's 
test,"  which  consists  in  converting  the  arsenic  into  arseniu- 
retted  hydrogen  in  a  similar  manner  to  that  employed  in 
the  case  of  antimony  about  to  be  described.  For  fuller 
details  of  "Marshes  test"  the  student  is  referred  to  any 
standard  work  on  General  Chemistry.  This  method  is 
applicable  to  the  detection  of  very  minute  quantities  of  arse- 
nic, and  owing  to  the  delicacy  of  the  test,  if  arsenic  is  present 
in  the  original  solution  some  trace  of  it  will  usually  appear 
in  the  test  for  antimony  here  described. 

The  insoluble  residue  containing  antimony  and  tin,  which 
was  left  on  the  filter,  is  washed  several  times  with  a  mix- 
ture of  equal  parts  of  alcohol  and  water,  and  then  trans- 
ferred to  a  test-tube  or  porcelain  dish  and  warmed  with 
strong  hydrochloric  acid.     Choose   a  cork  or  caoutchouc 


§25.]  SEPARATION  OF  ANTIMONY.  37 

stopper  provided  with  two  holes,  which  fits  accurately  the 
mouth  of  a  wide  test-tube.  Fit  a  small  thistle-tube  to  one 
of  the  holes,  and  to  the  other  a  short  bent  tube  drawn  to  a 
rather  fine  open  point.  Put  a  fragment  or  small  strip  of 
zinc  (App.,  §  57),  together  with  a  bit  of  platinum  foil  into 
the  tube,  cover  with  water,  close  the  tube  with  the  perforated 
stopper,  and  through  the  thistle-tube  add  strong  hydrochlo- 
ric acid  in  small  successive  portions.  After  hydrogen  has 
been  generated  freely  during  four  or  five  minutes  by  the 
mixture  in  the  tube,  and  all  the  air  originally  contained  in 
the  latter  has  been  expelled,  light  the  gas  issuing  from  the 
pointed  glass  tube,  and  pour  into  the  thistle-tube,  a  portion 
at  a  time,  the  mixture  of  strong  hydrochloric  acid  and  the 
residue  containing  antimony  and  tin,  or  the  solution  if  the 
acid  has  dissolved  the  residue  completely.  Hold  a  cold 
porcelain  dish  or  bit  of  broken  porcelain  in  the  flame,  taking 
care  to  shift  the  position  of  the  dish  frequently  so  that  fresh 
surfaces  of  porcelain  may  be  exposed  to  the  burning  gas. 
If  there  be  really  any  antimony  in  the  insoluble  residue,  an- 
timoniuretted  hydrogen  will  be  evolved,  together  with  free 
hydrogen,  and  characteristic  smoky-black  spots  or  stains  of 
metallic  antimony  will  be  deposited  from  it  upon  xest 
the  cold  porcelain.  To  be  sure  that  the  spots  are  for 
really  composed  of  antimony  and  not  of  arsenic,  ^*'- 
which  forms  arseniuretted  hydrogen  and  deposits  metallic 
arsenic  under  the  circumstances  in  which  antimoniuretted 
hydrogen  is  produced  and  deposits  antimony,  cover  them 
with  a  solution  of  hypochlorite  of  sodium  (App.,  §  63) :  if 
they  are  antimony  spots,  they  will  not  dissolve,  being  unaf- 
fected for  a  long  time,  while  arsenic  spots  dissolve  at  once. 
The  following  comparisons  of  arsenic  and  antimony  thus 
deposited  may  be  noticed.  The  arsenic  spots  have  a 
metallic  lustre  and  brown  color  when  thin;  the  stain  of 
antimony  has  a  feeble  lustre  and  is  smoky  black.  The 
arsenic  spot  disappears  readily  at  a  heat  below  redness;  the 


S8  SEPARATION  OF  ANTIMONY  AND   TIN,       [§  25. 

stain  of  antimony  is  volatile  only  at  a  red  heat.  The  arsenic 
spot  is  not  perceptibly  ali'ected  by  yellow  sulphide  of  am- 
monium unless  heated :  the  antimony  stain  dissolves  readily, 
a  bright  orange  stain  remaining  after  evaporation. 

In  order  not  to  explode  the  test-tube  on  lighting  the  gas, 
the  operator  must  wait  patiently  for  several  minutes,  until 
all  the  air  has  been  expelled  from  the  tube. 

The  whole  of  the  antimony  is  not  converted  by  this  means 
into  antimoniuretted  hydrogen ;  a  portion  is  reduced  to  the 
metallic  state,  and  if  the  evolution  has  not  been  too  rapid, 
will  be  found  deposited  on  the  platinum  foil  as  a  firmly  ad- 
herent dark  coating  or  stain.  Therefore  when  the  zinc  in 
the  test-tube  is  nearly  all  consumed,  transfer  the  contents 
of  the  tube  to  a  porcelain  dish  and  examine  the  platinum 
foil  for  this  indication  of  the  presence  of  antimony. 

To  confirm  the  presence  of  antimony  indicated  by  the 
black  stain  or  coating  on  the  platinum  foil,  warm  the  foil 
for  a  few  moments  with  strong  hydrochloric  acid  to  remove 
all  traces  of  tin,  wash  free  from  the  acid,  treat  with  a  few 
drops  of  dilute  nitric  acid  and  a  few  drops  of  tartaric  acid 
(App.,  §  14),  heat  nearly  to  boiling,  dilute  with  an  equal 
volume  of  water  and  pass  sulphuretted  hydrogen  through 
the  solution.  An  orange  precipitate  shows  the  presence  of 
antimony. 

In  the  operation  of  testing  for  antimoniuretted  hydrogen 
as  above  described,  the  tin  which  was  in  the  form  of  oxide 
was  reduced  to  the  metallic  state  and  now  awaits  examina- 
tion in  the  porcelain  dish.  Remove  and  rinse  any  zinc 
remaining  undissolved  and  carefully  decant  from  the  dark 

Test  spongy  mass  the  solution  with  which  it  is  covered, 
for       and  which   consists   mainly;?  of  chloride  of  zinc. 

S"-  The  residue  is  warmed  with  strong  hydrochloric 
acid,  in  which  the  tin  dissolves. 

Pour  off  the  solution  of  stannous  chloride  thus  obtained, 
and  add  to  it  a  few  drops  of  a  solution  of  mercuric  chloride 
(App.,  ^55):  a  white  or  gray  precipitate  of  mercurous  chlo- 


§§  26,  26.] 


S^PAttATlON   OF  TIN. 


89 


ride  often  mixed  with  gray  metallic  mercury  will  be  thrown 
down;  for  — 

2  HgCl^  +  SnClj  =  2  HgCl  +  SnCl,,  and  2  PIgCl  +  SnCl^  -  2  Hg  +  SnCl,. 

To  prove  that  the  precipitate  really  contains  mercurous 
chloride,  decant  the  supernatant  liquid;  cover  the  precipi- 
tate with  ammonia-water  and  heat  the  mixture  to  boiling 
(compare  j).  21).  A  black  residue  slowly  soluble  in  hot 
concentrated  hydrochloric  acid  is  often  obtained  when  no 
tin  is  present,  which  is  metallic  lead,  a  common  impurity  in 
zinc.  Enough  of  this  lead  may  dissolve  in  the  strong  hydro- 
chloric acid  to  give  a  white  precipitate  of  chloride  of  lead 
when  the  liquid  is  diluted  by  the  addition  of  the  solution  of 
mercuric  chloride.  Hence  it  is  always  best,  in  case  a  white 
precipitate  is  formed,  to  prove  that  it  is  really  mercurous 
chloride  by  treating  with  ammonia-water  as  described. 

A  black  residue  insoluble  in  strong  hydrochloric  acid 
may  be  metallic  gold  or  platinum  if  either  of  these  elements 
were  present  in  the  original  solution,  or  perhaps  it  may  be 
metallic  lead  from  the  impure  zinc. 

26.  An  outline  of  the  foregoing  operations  may  be  repre- 
s^ted  in  tabular  form  as  follows :  — 


The  General  Reao;ent  (H.^S)  of  Class  III  precipitates  As-^S.^, 
Sb.^S^  and  SnS  or  SnS,„  [An^^]  and  [EtB^].  (As  well  as  the 
members  of  Class  II  from  which  Class  III  is  separated  by  solution 
in  sulphide  of  sodium.)  The  sulphide  of  sodium  solution  is  treated 
with  nitric  acid  and  carbonate  of  sodium;  the  mixture  is  evaporated, 
mixed  with  carbonate  and  nitrate  of  sodium  and  heated  to  fusion. 
The  fused  mass  is  treated  with  cold  water. 


Arseniate  of  sodium 
(with  nitrate  of  sodium, 
etc.)  goes  into  solution. 
Confirm  presence  of  As 
by  magnesium  mixture 
and  by  the  silver  test. 


Antimoniate  of  sodium  and  oxide  of  tin 
remain  undissolved.  Reduce  with  zinc 
and  HCl  in  presence  of  platinum  foil. 


A  ntimoniuretted 
hydrogen  is  formed 
and  antimony  spots 
obtained. 


Tin  is  left  in  the 
metallic  state  (to- 
gether with  some  an- 
timony which  stains 
the  foil).  Dissolve 
the  tin  in  HCl  and 
test  with  HgCl.,, 


40         SEPARATION  OF  GOLD  AND  PLATINUM.     [§  26. 

In  the  case  of  mixtures  containing  gold  and  platinum  (see 
§  13),  as  well  as  arsenic,  antimony  and  tin,  the  gold  and 
platinum  would  remain  with  the  tin,  without  interfering  in 
any  way  with  the  separation  or  detection  of  either  member 
of  the  class,  and  when  the  tin  reduced  by  zinc  is  dissolved 
in  hydrochloric  acid,  the  gold  and  platinum  would  remain 
undissolved  (together  with  some  antimony,  if  present). 
Since  the  sulphides  of  gold  and  platinum  are  both  black, 
while  those  of  arsenic  and  tin  are  yellow  or  brown,  and  that 
of  antimony  is  orange,  the  presence  of  any  considerable 
quantity  of  either  of  the  precious  metals  would  be  indicated 
by  the  black  color  of  the  class  precipitate. 

There  are  excellent  special  tests  both  for  gold  and  for 
platinum,  by  which  these  elements  may  be  detected  even  in 
the  presence  of  all  the  other  metals.  Hence  it  is  most  con- 
venient to  make  special  search  for  them  in  the  original 
substance,  by  methods  to  be  described  hereafter  (§  98,  6), 
whenever  the  preliminary  examination  has  given  reason  to 
suspect  the  presence  of  either  of  them. 

In  the  regular  course  of  analysis  these  elements  may  be 
detected  by  the  following  method. 

Wash  the  black  residue  insoluble  in  concentrated  hydro- 
chloric acid  thoroughly  free  from  acid;  add  to  it  a  few 
drops  of  nitric  acid  and  of  tartaric  acid;  heat  gently  to 
remove  any  antimony  that  may  be  present  in  metallic  con- 
dition; wash  thoroughly;  heat  the  black  residue  in  an 
evaporating-dish  with  a  little  aqua  regia;  evaporate  to  a 
small  volume;  add  a  few  drops  of  chloride  of  ammonium; 

Test  evaporate  nearly  to  dryness  at  a  gentle  heat,  and 
for  treat  the  residue  with  a  teaspoonful  or  so  of  a  mix- 
^*-  ture  of  equal  parts  alcohol  and  water.  A  yellow 
residue  appearing  crystalline  under  the  microscope  indi- 
cates platinum. 

Eemove  the  platinum,  which  is  in  the  form  of  chloro- 
platinate  of  ammonium,  by  filtering  through  a  small  filter, 


§§  26,27.]  ALTEttNATtVM  METHOD  FOU  CLASS  III.     41 

warm  gently  to  remove  the  alcohol,  and  add  a  few  drops  of 
oxalate  of  ammonium  solution  and  of  oxalic  acid;      ^pest 
a  brown  or  violet  precipitate  often  forming  slowly      for 
indicates  gold,  separating  in  the  metallic  condition.      '^^• 

27.  As  considerable  difficulty  is  often  experienced, 
especially  by  beginners,  in  analyzing  the  mixed  sulphides 
of  this  class,  the  following  method  of  treatment  is  suggested 
as  an  alternative. 

To  effect  the  separation :  —  Add  dilute  hydrochloric  acid 
in  small  portions  to  the  sulphide  of  sodium  solution  until 
the  reaction  is  distinctly  acid.  The  sulphides  of  arsenic, 
antimony  and  tin  are  precipitated,  together  with  some 
free  sulphur.  Any  large  excess  of  acid  is  to  be  avoided 
lest  the  sulphides  of  antimony  and  tin,  which  are  some- 
what soluble  in  hydrochloric  acid,  fail  to  be  precipitated. 

Collect  the  precipitate  on  a  filter  and  throw  the  filtrate 
away.  The  precipitate  is  rinsed  with  water,  transferred 
to  a  test-tube  or  small  flask,  covered  with  strong  hydro- 
chloric acid,  and  gently  warmed,  not  boiled.  The  yellow 
residue  is  sulphide  of  arsenic.  The  antimony  and  tin  pass 
into  the  filtrate  as  chlorides.  To  test  for  these  elements, 
prepare  a  small  hydrogen-generator,  as  described  at  the 
top  of  page  37,  and  test  for  the  elements  as  there  directed, 
taking  care  to  warm  the  hydrochloric  acid  solution  to  drive 
off  all  traces  of  sulphuretted  hydrogen  before  placing  it  in 
the  hydrogen-generator. 

To  test  for  arsenic,  transfer  the  sulphide  of  arsenic  which 
did  not  dissolve  in  the  strong  hydrochloric  acid  to  a  small 
flask,  add  a  teaspoonful  of  strong  nitric  acid,  and  warm 
gmtly  for  several  minutes.  Then  add  in  small  successive 
])ortions  chlorate  of  potassium,  using  in  all  an  amount  no 
larger  than  half  a  pea. 

When  the  sulphide  of  arsenic  has  entirely  dissolved, 
pour  the  liquid  into  an  evaporating-dish  and  warm  gently 
until  the  chlorous  smell  has  disappeared.     This  treatment 


42       SEPARATION   OF  CLASSES  It  AND  lit.     [§§  27,  28. 

for  arsenic  must  be  carried  on  where  there  is  a  good  draught, 
and  the  acid  must  be  warmed,  not  boiled.  When  the  chlo- 
rous fumes  have  been  driven  off,  add  ammonia-water  until 
the  reaction  is  alkaline,  filter,  if  necessary,  and  to  the  clear 
alkaline  liquid  add  a  small  quantity  of  a  prepared  solution 
of  chloride  of  magnesium  and  chloride  of  ammonium  (App., 
§  48),  and  set  the  mixture  aside  for  twelve  hours.  The 
formation  of  a  white  crystalline  precipitate  of  arseniate  of 
ammonium  and  magnesium  is  evidence  of  the  presence  of 
arsenic. 

In  this  method,  if  gold  and  platinum  be  present,  they 
will  be  found  in  the  solution  containing  the  arsenic;  and  if 
a  black  residue  remains  after  warming  with  strong  hydro- 
chloric acid,  dissolving  on  addition  of  chlorate  of  potassium 
and  nitric  acid,  a  portion  of  the  solution  should  be  tested 
for  these  elements. 

To  test  for  gold  and  platinum,  evaporate  a  portion  of  the 
solution  obtained  as  described  almost  to  dryness,  prepare  a 
small  hydrogen-generator  as  in  testing  for  antimony  and 
tin,  and  add  this  solution,  with  some  strong  hydrochloric 
acid,  which  may  contain  arsenic,  gold  and  platinum,  just 
as  the  solution  of  antimony  and  tin  was  added.  Test  the 
ignited  gas  for  arsenic  as  described  in  the  test  for  antimony. 
Gold  and  platinum  will  remain  in  the  generator  and  may  be 
tested  for  as  previously  described. 

28.  The  Method  of  Separating  Class  II  from  Class  HI  has 
been  sufficiently  described  in  §§  8,  24.  When  members  of 
Class  II  are  altogether  absent,  something  may  be  learned 
from  the  color  of  the  precipitate  produced  by  sulphuretted 
hydrogen.     Thus,  — 

An  orange-colored  precipitate  indicates  the  presence  of 
antimony; 

A  bright  yellow  precipitate,  the  presence  of  arsenic; 

A  dull  yellow  precipitate,  white  at  first,  the  presence  of 
stannic  sulphide; 


§  28.]       SEPARATION   OF  CLASSES  II  AND  III  43 

A  dark  brown  precipitate,  the  presence  of  stannous  sul- 
phide ; 

A  black  precipitate,  the  presence  of  gold  or  platinum. 

When,  as  a  result  of  the  preliminary  examination  (§  82, 
III,  cl),  there  is  reason  to  suspect  the  presence  of  mercury 
as  a  mercuric  salt,  sulphide  of  ammonium  which  has  become 
yellow  from  standing,  should  be  substituted  for  sulphide  of 
sodium,  because  sulphide  of  mercury  is  somewhat  soluble 
in  sulphide  of  sodium  This  may  be  seen  by  taking  a  few 
drops  of  mercuric  chloride  solution,  adding  an  equal  volume 
of  water  and  two  or  three  teaspoonfuls  of  sodium  sulphide 
solution.  Boil,  and  filter  if  necessary.  To  a  portion  of  the 
clear  filtrate  add  dilute  nitric  acid  and  observe  the  color  of 
the  precipitate.  Repeat  the  experiment,  using  sulphide  of 
ammonium  instead  of  sulphide  of  sodium.  In  the  event 
of  the  analysis  of  an  unknown  solution,  if  on  the  treat- 
ment with  nitric  acid  of  the  solution  of  sulphides  in  sul- 
phide of  sodium,  a  black  precipitate  appear,  it  may  be  owing 
to  the  presence  of  sulphide  of  mercury,  and  not  to  gold  and 
platinum;  it  is  therefore  sometimes  better  in  such  a  case  to 
dilute  the  solution  with  water,  filter  and  treat  the  precipi- 
tate with  sulphide  of  ammonium.  The  precipitate  remain- 
ing undissolved  is  added  to  the  regularly  obtained  precipi- 
tate of  Class  II,  and  the  sulphide  of  ammonium  solution 
added,  with  a  fresh  portion  of  strong  acid,  to  the  nitric  acid 
solution  already  obtained. 

If  the  second  method  has  been  employed,  any  sulphide  of 
mercury  dissolved  by  the  sulphide  of  sodium  will  remain 
with  the  sulphide  of  arsenic.  In  case,  therefore,  this  resi- 
due is  black  or  dark  colored,  it  may  be  owing  to  the  presence 
of  mercury,  and  not  to  gold  or  platinum.  For  this  reason, 
it  may  be  advisable  in  such  a  case  to  test  the  dark-colored 
residue  with  sulphide  of  ammonium.  The  residue  remain- 
ing undissolved  is  added  to  the  regular  Class  II  precipitate, 
the  sulphide  of  arsenic  is  reprecipitated  by  the  addition  of 


44  SEPARATION   OF  CLASSES  II  AND  III        [§  28. 

hydrochloric  acid  to  the  alkaline  solution,  and  the  precipi- 
tate tested  for  arsenic  as  described. 

If  an  abundant  supply  of  the  substance  under  examina- . 
tion  be  at  hand,  it  will  often  be  better  to  start  with  a  fresh 
portion   and  make  the  separation  of  the  two  classes  with 
sulphide  of  ammonium. 

The  separation  of  the  members  of  Class  III  from  the 
other  elements  precipitated  by  sulphuretted  hydrogen  in 
acid  solutions  depends  upon  the  formation  of  sulphur  salts, 
of  arsenic,  antimony,  etc.,  when  their  sulphides  are  treated 
with  alkaline  sulphides,  which  are  in  most  cases  readily 
soluble. 

In  the  course  of  a  general  analysis  of  a  solution  contain- 
ing members  of  both  the  second  and  third  classes,  it  is 
essential  that  the  precipitate  produced  by  sulphuretted  hy- 
drogen should  be  washed  free  from  acid  to  prevent  decom- 
position of  the  alkaline  sulphides  and  introduction  of 
complications  thereby.  Sulphide  of  copper  is  somewhat 
soluble  in  solutions  of  the  normal  sulphides  of  ammonium 
and  sodium,  acids  reprecipitating  it  sometimes  as  a  light- 
colored  sulphide,  which,  with  excess  of  sulphur,  has  nearly 
the  color  of  stannous  sulphide  or  of  arsenious  sulphide. 
Some  loss  may  thus  result,  but  enough  of  the  sulphide, 
which  is  entirely  insoluble  in  the  yellow  sulphide  of  sodium 
(sodium  polysulphide,  Na.^S^),  will  usually  remain  undis- 
solved to  insure  the  detection  of  copper  in  Class  II.  As 
with  mercury,  the  preliminary  examination  (§  81)  is  of  value 
in  this  case  also. 

The  normal  colorless  sulphides  of  ammonium  and  sodium 
usually  fail  to  dissolve  stannous  sulphide,  as  an  excess  of 
sulphur  is  necessary  for  the  formation  of  the  soluble  sul- 
phostannates. 

SnS  +  NajSj  =  NajSnSj. 

Sulphide  of  ammonium  is  in  general  not  so  fit  a  solvent 


§  28.]       SEPARATION   OF  CLASSES  II  AND  TIL  45 

for  the  sulphides  of  Class  III  as  sulphide  of  sodium;  and  if 
the  presence  of  tin  is  suspected,  it  is  necessary  to  use  the 
yellow  or  polysulphide,  or  else  add  a  little  sulphur  as  men- 
tioned. In  any  case  it  is  important  to  use  no  more  of  the 
alkaline  sulphide  than  is  necessary,  on  account  of  the 
amount  of  sulphur  which  will  have  to  be  oxidized  subse- 
quently with  nitric  acid  and  nitrate  of  sodium. 


CHAPTER  V. 

CLASS  IV.  — ELEMENTS  WHOSE  HYDRATES  ARE  INSOLU- 
BLE IN  WATER,  AMMONIA-WATER  AND  SOLUTIONS  OF 
AMMONIUM    SALTS. 

29.  The  leading  fact  upon  which  the  separation  of 
this  class  is  based  is  the  insolubility  of  the  hydrates  of 
iron,  aluminum  and  chromium  in  ammonia- water,  even  in 
presence  of  solutions  of  ammonium  salts.  But  these 
three  hydrates  are  not  the  only  substances  which  are  liable 
to  be  precipitated  in  an  actual  analysis  when  ammonia- 
water  is  added  in  excess  to  a  solution  previously  acid. 
There  are  a  number  of  compounds,  soluble  in  acids,  but  not 
in  water  or  in  weak  alkaline  liquids,  which  are  thrown 
down  without  change  when  their  acid  solvent  is  destroyed. 

It  is  clear  that  it  is  needless  to  provide  in  this  place 
against  the  presence  of  such  salts  of  elements  belonging  to 
Classes  I,  II  and  III.  Those  elements  are  already  elimi- 
nated when  the  fourth  class  is  taken  in  hand.  But  if  there 
are  any  salts  of  elements  belonging  to  the  fourth  and  higher 
classes  which  can  only  be  kept  in  solution  by  a  free  acid, 
they  will  be  precipitated  without  change  in  consequence  of 
the  neutralization  of  their  solvent  by  the  ammonia-water 
added  to  precipitate  the  three  hydrates  above  mentioned. 
Such  salts  are  the  phosphates  of  several  members  of  Classes 
IV,  VI  and  VII,  besides  a  number  of  oxalates,  borates, 
silicates  and  fluorides  which  occur  so  seldom  that  they 
need  not  be  particularly  considered  in  an  elementary  treatise. 
Beside  the  phosphates,  several  chromites  and  aluminates  of 
members  of  Classes  VI  and  VII  are  insoluble  in  ammonia- 


§§  29-31.]         PRECIPITATION  OF  CLASS  IV.  47 

water,  and  are  often  thrown  down  wholly  or  in  part  along 
with  the  legitimate  members  of  Class  IV.  Manganese  also 
(a  member  of  Class  V)  is  frequently  precipitated  in  com- 
bination with  members  of  Class  IV,  in  the  form  of  chromite, 
ferrite  or  aluminate  of  manganese.  The  general  scheme 
for  the  examination  of  Class  IV  necessarily  provides  for 
the  detection  of  all  the  members  of  the  class  in  the  possible 
presence  of  these  extraneous  substances. 

30.  Example  of  the  Precipitation  with  Ammonia-water.  — 
Pour  into  a  beaker  a  small  teaspoonful  of  aqueous  solu- 
tions (App.,  §  Q>Q))  of  sulphate  of  manganese,  common  alum 
(sulphate  of  aluminum  and  ammonium),  chrome  alum  (sul- 
phate of  chromium  and  potassium)  and  chh)ride_of ,  iron 
(ferrous  chloride).  As  an  example  of  the  substances  insol- 
uble in  water  which  might  be  present  in  an  acid  solution, 
dissolve  in  a  small  amount  of  boiling  hydrochloric  acid,  a 
not  very  large  quantity,  say  half  a  gramme,  of  bone-ash 
(phosphate  of  calcium),  and  add  the  solution  to  those 
already  placed  in  the  beaker.  Fill  the  beaker  about  one 
third  full  of  water,  heat  the  mixture  to  boiling,  and  add  to 
it  two  or  three  drops  of  strong  nitric  acid  to  convert  the 
iron  into  ferric  salts.  Boil  the  mixture  for  a  minute  or 
two  and  then  add,  little  by  little,  ammonia-water  to  the 
boiling  liquor  until  a  distinct  odor  of  ammonia  is  percepti- 
ble after  the  mixture  has  been  thoroughly  stirred. 

31.  Analysis  of  the  Mixed  Precipitate.  —  The  following 
method  of  detecting  iron,  chromium,  aluminum  (and  man- 
ganese) in  the  mixed  precipitate  which  may  contain  all  of 
them,  together  with  phosphates  and  other  compounds  of 
barium,  strontium,  calcium  and  magnesium,  depends:  — 
1st.  Upon  the  oxidation  and  conversion  of  the  hydrates  of 
manganese  and  chromium  into  manganate  and  chromate  of 
sodium  (or  potassium)  when  fused  with  a  mixture  of  car- 
bonate of  sodium  and  nitrate  of  potassium;  while  the 
hydrate  of  aluminum  under  the  same  treatment  is  converted 


48  SEPARATION   OF  CLASS  IV.  [§  31. 

to  a  greater  or  less  extent,  into  aluminate  of  sodium,  and 
the  compounds  of  barium,  strontium  and  calcium  either 
remain  unchanged  or  are  converted  into  carbonates.  2d. 
Upon  the  solubility  of  the  chromate  and  aluminate  of 
sodium  (or  potassium)  in  water  and  the  insolubility  of  the 
carbonates  or  other  compounds  of  barium,  strontium  and 
calcium  which  may  be  present  in  the  fused  mass. 
3d.  Upon  the  sparing  solubility  of  chromate  of  lead  in 
acetic  acid.  4th.  Upon  the  peculiar  green  color  of  the 
manganate  of  sodium  (or  potassium).  5th.  Upon  the  fact 
that  Prussian  blue  is  formed  when  a  solution  of  ferro- 
cyanide  of  potassium  is  added  to  the  solution  of  a  ferric 
salt.  6th.  Upon  the  sparing  solubility  of  the  oxalates  of 
barium,  strontium  and  calcium  in  dilute  acetic  acid. 
—  The  details  of  the  treatment  of  the  precipitate  produced 
by  ammonia-water,  are  as  follows :  —  Collect  the  precipitate 
upon  a  filter,  wash  it  two  or  three  times  with  water,  and 
then  dry  it  either  on  the  filter,  or  by  transferring  it  to  a 
piece  of  platinum  foil  or  to  a  platinum  crucible  (App.,  §  84) 
and  heating  over  the  lamp  gently  so  as  to  avoid  spattering. 
The  dry  precipitate  is  mixed  intimately  (best  by  rubbing 
in  a  mortar)  with  five  or  six  times  its  bulk  of  a  dry  mixture 
of  equal  parts  of  carbonate  of  sodium  and  nitrate  of  potas- 
sium (App.,  §  37).  The  mixture  is  then  fused  thoroughly 
by  heating  it  over  the  lamp  either  on  platinum  foil  or  in 
a  platinum  crucible.  If  the  amount  of  the  mixture  be 
small,  a  piece  of  foil  answers  very  well;  larger  quantities 
may  be  fused  in  successive  portions  on  the  foil,  but  a  small 
crucible  is  much  more  convenient. 

If  only  a  manganese  compound  and  no  chromium  had  been 
fused  on  the  foil,  the  cold  mass  would  have  exhibited  the 
peculiar  bluish-green  color  of  manganate  of  sodium  (or 
potassium)  owing  to  the  oxidation  of  a  small  portion  of 
the  hydrate  of  manganese  to  manganic  acid  in  the  presence 
of  carbonate  of  sodium  and  nitrate  of  potassium.     If  only 


§  31.]       SEPABATION  OF  CHROMIUM.  49 

chromium  had  been  present,  the  bright  yellow  color  of 
chromate  of  sodium  (or  potassium)  would  have  been  clearly 
perceived.  But  from  mixtures  of  the  manganate  and  chro- 
mate of  sodium  (or  potassium),  in  various  proportions,  dif- 
ferent shades  of  green,  brownish-green  or  yellowish-green, 
will  result.  When  iron  is  present,  the  red  color  of  its  oxide 
may  obscure  the  colors  due  to  manganese  and  chromium.  . 

Place  the  platinum  foil  or  crucible  in  a  porcelain  dish, 
cover  it  with  water,  and  boil  the  latter  until  all  the  soluble 
matter  has  been  dissolved  from  the  foil.  Take  out  the 
foil,  rinse  it,  and  throw  the  contents  of  the  dish  upon  a 
filter.  The  manganate,  chromate  and  aluminate  of  sodium 
pass  into  the  filtrate,  along  with  the  excess  of  the  carbonate 
of  sodium  and  nitrate  of  potassium  employed :  the  filtrate 
is  colored  yellow  by  the  chromate.  The  insoluble  residue, 
in  this  case,  consists  of  the  oxides  of  iron  and  manganese, 
together  with  the  phosphate  of  calcium  which  has  not  been 
altered  by  the  fusion,  and  any  small  portion  of  carbonate 
of  calcium  which  may  have  been  formed  by  the  decomposi- 
tion of  a  part  of  the  phosphate.  In  the  case  of  an  actual 
analysis  there  might  be  also  phosphates,  carbonates  and 
other  insoluble  compounds  of  barium,  strontium  and  mag- 
nesium, as  well  as  of  aluminum,  iron,  etc. 

Divide  the  filtrate   from  the   insoluble   residue   of  the 
fusion  into  two  portions.     Carefully  add  acetic  acid,  drop 
by  drop,  to  one  of  these  portions  until  the  liquor  exhibits 
an  acid  reaction,  after  all  carbonic  acid  is  set  free,  and  then 
add  to  it  two  or  three  drops  of   a  solution  of  acetate  of 
lead  (App.,  §  46).     An  insoluble  precipitate  of  chromate  of 
lead  will  be  immediately  thrown  down,  exhibiting  a  bright 
yellow  color  if  the  reagents  be  all  pure.     But  if,  as  often 
happens,  the  carbonate  of  sodium,  employed  as     Test 
the  flux,  is  contaminated  with  sulphate  of  sodium,       for 
the    yellow  color    of    the    precipitate   will    tend      ^^• 
towards  white,  in  proportion  to  the   amount  of  sulphate 


J 


60  SEPARATION   OF  ALUMINUM.  [§  3L 

of  lead  which  has  gone  down  together  with  the  chromate. 
A  pure  white  precipitate  would  be  no  indication  of 
chromium,  but  only  of  a  sulphate  in  the  reagents. 

Acidulate  the  other  portions  of  the  aqueous  solution  of 
the  fused  sodium  (and  potassium)  compounds  with  dilute 

Test  hydrochloric  acid,  add  ammonia-water  to  slight 
for  alkaline  reaction,  warm  the  mixture  and  leave  it 
•^^-  at  rest  for  at  least  half  an  hour  or,  better,  over 
night.  After  the  lapse  of  some  time,  a  characteristic,  gelat- 
inous, colorless  agglomeration  of  particles  of  hydrate  of 
aluminum  will  appear  at  the  top  or  bottom  of  the  liquid. 

It  should  be  said,  that  flocks  of  hydrate  of  aluminum, 
when  diffused  through  a  liquid,  are  almost  transparent 
enough  to  elude  observation.  When  an  acid  solution,  con- 
taining much  aluminum,  is  mixed  with  ammonia-water  and 
warmed,  a  copious  precipitate  of  hydrate  of  aluminum  will 
appear  immediately,  and  will  often  remain  floating  for 
some  time  upon  the  surface  of  the  solution  by  virtue  of 
bubbles  of  air  entangled  in  it.  But  since  it  is  not  easy  to 
convert  the  whole  of  the  alumina  in  the  original  precipitate 
into  soluble  aluminate  of  sodium,  by  fusion  with  carbonate 
of  sodium  in  the  method  above  described,  the  quantity  of 
the  hydrate  to  be  thrown  down  at  the  final  test  is  often 
very  small,  and  considerable  time  must  be  allowed,  in 
order  that  every  particle  of  it  may  separate  from  the  solu- 
tion, and  all  the  particles  collect  into  a  single  mass. 

To  confirm  the  presence  of  aluminum,  collect  the  hydrate 
in  the  point  of  a  small  filter  and  allow  it  to  drain.  Cut 
away  the  superfluous  paper,  place  that  portion  of  the  filter 
to  which  the  precipitate  is  attached  upon  a  piece  of  char- 
coal, and  heat  it  intensely  in  the  blowpipe  flame.  Moisten 
the  residue  with  a  drop  of  a  solution  of  nitrate  of  cobalt 
and  again  ignite  it  strongly.  The  unfused  compound  of 
aluminum,  cobalt  and  oxygen  left  upon  the  coal  will  exhibit 
a  deep  sky-blue  color  when  allowed  to  cool.     This  reaction 


§  31.]     SEPARATION  OF  MANGANESE  AND  IBON.         51 

is  useful  in  distinguishing  the  hydrate  of  aluminum  from 
that  of  glucinum,  an  element  somewhat  similar  to  alu- 
minum though  far  less  abundant.  Hydrate  of  glucinum 
when  ignited  with  nitrate  of  cobalt  does  not  yield  a  pure 
blue  compound,  but  only  a  gray  mass.  Silica  gives  a  very 
faint  blue  tint. 

Eeturn  now  to  the  insoluble  residue  of  the  fusion  with 
carbonate  of  sodium  and  nitrate  of  potassium.  If  the  char- 
acteristic color  of  the  manganate  of  sodium  (or  potassium) 
were  not  distinctly  observed  at  the  previous  fusion,  take 
a  small  quantity  of  the  insoluble  residue  and  fuse  it  with 
twice  its  bulk  of  a  mixture  of  carbonate  of  sodium  and 
nitrate  of  potassium  upon  platinum  foil  in  a  strong  oxidizing 
blowpipe  flame  (App.,  §  82).  The  peculiar  bluish-green 
coloration  of  manganate  of  sodium  will  appear  ^^g^ 
in  the  fused  mass,  as  soon  as  it  has  become  cold,  for 
particularly  at  the  edges  and  thinner  portions.  In  MSL- ~ 
thus  testing  for  manganese,  it  is  well  to  incline  the  foil,  so 
that  portions  of  the  thoroughly  melted  mass  may  flow  away 
from  the  centre  of  the  mixture  into  thin  sheets,  in  order  that 
the  color  of  the  manganate  may  be  exhibited  in  its  purity. 

Boil  a  second  small  portion  of  the  insoluble  residue  with 
a  little  strong  hydrochloric  acid,  dilute  the  solution  with 
water,  and  add  a  drop  or  two  of  ferrocyanide  of  potassium. 
The  liquid  will  immediately  become  colored  with      xest 
Prussian  bine,   an  indication  of  the  presence  of      for 
iron.     In  case  much  iron  be  present,  the  blue  color     1!®- 
may  be  too  deep  to  be  recognized  until  the  liquid  has  been 
diluted  with  a  large  quantity  of  water. 

Warm  another  portion  of  the  insoluble  residue  with  a 
few  drops  of  acetic  acid,  dilute  the  solution  with  water, 
and  filter  if  anything  remain  undissolved.  To  the  slightly 
acid  liquid  add  a  teaspoonful  of  a  solution  of  oxalate  of 
ammonium  (App.,  §  21).  Any  compounds  of  barium,  stron- 
tium and  calcium  which  may  have  been  present  in  the  resi- 


52  SEPARATION   OF  CLASS  IV.  [§§  31,  32. 

due  will  be  deposited  as  oxalates,  as  the  oxalates  of  these 
elements  are  but  sparingly  soluble  in  acetic  acid.  In  the 
prfesent  case  there  will  be  a  precipitate  of  oxalate  of  cal- 
cium. Allow  the  mixture  to  stand  for  some  time,  and  finally- 
collect  the  precipitate  on  a  filter,  wash,  dry  and  preserve 
it  for  future  examination  in  connection  with  Class  VI. 

In  addition  to  the  elements  present  in  the  solution  which 
has  just  been  analyzed,  compounds  of  magnesium  are  also 
under  certain  circumstances  precipitated  with  the  hydrates 
of  Class  IV.  In  actual  practice,  therefore,  the  remainder 
of  the  insoluble  residue  is  examined  for  magnesium,  as  fol- 
lows :  —  Heat  the  mixture  strongly  on  the  platinum  foil  so 
as  to  render  the  oxides  of  aluminum  and  iron  as  insoluble 
as  possible,  and  then  treat  with  dilute  hydrochloric  acid 
and  warm  gently.  Without  regarding  the  matter  which 
remains  undissolved  add  to  the  mixture  (which  contains  in 
solution,  along  with  the  magnesium,  some  iron,  aluminum, 
calcium,  etc.)  a  teaspoonful  of  chloride  of  ammonium,  and 
ammonia- water  to  alkaline  reaction.  Throw  the  mixture 
upon  a  filter,  collect  the  filtrate,  and  add  it  to  that  origi- 
nally obtained  from  the  precipitate  of  Class  IV :  this  mixed 
filtrate  will  be  examined  in  due  course  (Class  VII)  for 
magnesium.  In  case  the  whole  amount  of  the  residue 
from  the  fusion  of  the  precipitate  of  the  class  with  car- 
bonate of  sodium  and  nitrate  of  potassium  be  but  small,  it 
is  well  to  filter  the  liquid  of  the  preceding  paragraph  which 
contains  the  precipitated  oxalates  of  barium,  strontium  and 
calcium,  to  evaporate  the  filtrate  to  dryness  and  ignite  to 
destroy  the  oxalic  and  acetic  acids.  The  residue  is  subse- 
quently treated  with  hydrochloric  acid,  chloride  of  am- 
monium and  ammonia,  filtered  and  the  filtrate  added  to  the 
filtrate  from  the  original  Class  IV  precipitate. 

32.  An  outline  of  the  foregoing  operations  may  be  tabu- 
lated as  follows :  — 


§32.] 


SEPARATION  OF  CLASS  IV. 


53 


The  General  Reagent  ([NHJHO  mixed  with  NH^Cl)  of  Class 
IV  precipitates  the  hydrates  of  Fe,  Cr  and  Al  together  with  Mn 
(as  a  chromite,  ferrite  or  aluminate),  and  various  phosphates  and 
other  compounds  of  Fe,  Cr,  Al,  Ba,  Sr,  Ca  and  Mg.  The  pre- 
cipitate is  dried  and  fused  with  Na-^COg  and  KNO3 ;  the  fused 
mass  is  treated  with  water,  and  filtered :  — 


Divide  the  filtrate  into  two 
portions :  — 


Divide   the   precipitate   into  four 
portions :  — 


Yellow  color 
of  the  solution 
indicates  Cr. 
Confirm  Cr  by 
precipitation 
of  PbCrO,. 


Acidulate 
with  HCl  and 
add  (NH4) 
HO.  Color- 
less flocculent 
precipitate 
proves  pres- 
ence of  Al. 


Test 
for  Mn 
by  fus- 
ing with 
Na^COs 

and 
KNO,. 


Test  for 
Fe  with 
ferrocy- 
anide  of 
potas- 
sium. 


Test  for 
Ca,  etc., 
by  pre- 
cipita- 
tion of 
the  oxa- 
lates 
from 
acetic 
acid  so- 
lution. 


Elimi- 
nate Mg 
by  dis- 
solving 
in  HCl 
and  re- 
precipi- 
tating 
Class  IV 
with 
NH^ 
HO. 


In  the  actual  examination  of  an  unknown  substance,  the 
analysis  is  somewhat  simplified,  if  the  substance  be  a  solid 
soluble  in  water,  or  if  it  be  a  neutral  solution,  or  if  by  any 
other  means  we  know  that  the  phosphates,  oxalates,  etc., 
mentioned  above  are  absent.  The  treatment  in  such  a  case 
may  be  simplified  by  the  omission  of  those  operations  look- 
ing to  the  separation  of  calcium,  barium,  etc.,  from  the 
residue  of  the  fusion  with  carbonate  of  sodium  and  nitrate 
of  potassium.  In  the  course  of  an  analysis  in  case  a  white 
precipitate  falls  on  the  addition  of  'the  general  reagent  of 
Class  ly,  phosphoric  and  oxalic  acids  should  be  tested  .for 
at  once  (§§  66  and  67).  Phosphate  of  aluminum  is  not 
easily  decomposed  by  the  fusion,  nor  is  it  soluble  in  acetic 
acid,  and  it  may  remain  as  an  insoluble  residue  after 
treating  the  fused  mass  with  water.  In  case,  therefore,  a 
white  residue  remains  insoluble  in  water  and  acetic  acid, 
it  may  be  tested  for  aluminum  by  heating  with  nitrate  of 
cobalt  on  charcoal,  as  described  in  the  confirmatory  test  for 


54  FERROUS  AND  FERRIC  SALTS.        [§§  32, 33. 

aluminum.  Magnesium  compounds  give  a  flesh  red  or  pink 
colored  mass  by  this  treatment. 

To  determine  whether  the  iron  in  the  substance  subjected 
to  analysis  was  originally  in  the  state  of  a  ferric  or  a  fer- 
rous salt,  test  a  small  quantity  of  the  original  solution 
with  a  drop  of  ferricyanide  of  potassium  (App.,  §  35).  The 
formation  of  Prussian  blue  proves  the  presence  of  a  ferrous 
salt.  Another  small  portion  of  the  original  solution,  tested 
with  a  drop  of  ferrocyanide  of  potassium,  would  yield  Prus- 
sian blue  in  case  the  solution  contained  a  ferric  salt.  In 
applying  either  of  these  tests  the  blue  coloration,  indica- 
tive of  iron,  is  alone  to  be  looked  for;  no  notice  need  be 
taken  of  other  colorations,  or  of  precipitates  formed  by  the 
action  of  the  ferri-  or  ferro-cyanide  upon  the  various  metal- 
lic salts  which  the  solution  may  contain.  The  possibility 
that  a  ferrous  salt  may  have  been  changed  into  a  ferric 
during  the  process  of  getting  the  original  substance,  if  a 
solid,  into  solution,  must  not  be  lost  sight  of. 

33.  Separation  of  Class  IV  from  Class  III.  The  methods 
of  eliminating  Classes  I,  II  and  III  from  mixtures  which 
contain  members  of  these  classes  as  well  as  of  Class  IV, 
have  already  been  described  in  §§  6  and  8. 

It  is  essential  to  the  success  of  the  operation  that  all 
the  sulphuretted  hydrogen  in  the  filtrate  from  Classes  II 
and  III  be  expelled,  for  sulphuretted  hydrogen  precipitates 
all  the  members  of  Classes  IV  and  V  from  alkaline  solu- 
tions, and  the  filtrate  now  in  question  is,  of  course,  made 
alkaline  when  ammonia-water  is  added  to  it.  The  conver- 
sion of  the  iron  into  a  ferric  salt  (by  means  of  nitric  acid) 
is  necessary  because  ferrous  hydrate  is  somewhat  soluble 
in  ammonium  salts,  and  could  not,  therefore,  be  precipi- 
tated completely  by  ammonia-water  in  the  acid  filtrate  from 
Classes  II  and  III. 

No  matter  what  the  condition  of  the  iron  may  have  been 
in  the  original  solution,  it  is  reduced  to  the  state  of  fer- 


§  33.]  FERROUS  AND  FERRIC  SALTS.  55 

rous  salts  by  sulphuretted  hydrogen.  The  filtrate  from  the 
precipitate  produced  by  sulphuretted  hydrogen  (the  general 
reagent  of  Classes  II  and  III)  should,  therefore,  be  placed 
in  a  porcelain  dish,  and  boiled,  until  the  steam  from  it 
ceases  to  blacken  lead  paper.  After  the  sulphuretted 
hydrogen  has  been  expelled,  three  or  four  drops  of  strong 
nitric  acid  must  be  added  to  the  liquid,  and  the  mixture 
boiled  for  a  moment  longer  to  convert  the  iron  into  ferric 
salts.  If  by  accident  the  student  should  fail  to  convert  the 
iron  entirely  to  the  state  of  a  ferric  salt,  there  will  be  pro- 
duced a  greenish,  slimy  precipitate  of  ferrous  hydrate  on 
the  addition  of  the  ammonia-water.  This  substance  may 
be  seen  by  adding  an  excess  of  ammonia-water  to  a  tea- 
spoonful  of  ferrous  chloride  solution.  Such  a  precipitate 
must  not  be  confounded  with  the  green  hydrate  of  chro- 
mium :  it  should  be  redissolved  in  nitric  acid  and  the  acid 
solution  boiled  anew  for  a  few  minutes  before  reprecipitat- 
ing  with  ammonia-water. 

When  all  the  iron  has  been  converted  to  the  state  of  a 
ferric  salt,  a  small  quantity  of  a  solution  of  chloride  of 
ammonium  is  added  to  the  boiling  liquid,  and  finally  am- 
monia-water, little  by  little,  with  constant  stirring,  until 
a  persistent  odor  of  ammonia  is  perceptible.  A  large  excess 
of  ammonia  must  be  carefully  avoided,  for  hydrate  of  alumi- 
num, being  somewhat  soluble  in  ammonia-water,  might  be 
kept  in  solution,  to  the  disturbance  of  the  analysis  of  Classes 
VI  and  VII. 

Chromium,  if  present  in  the  original  substance  in  the 
form  of  a  chromate,  must  undergo  reduction  by  the  action 
of  sulphuretted  hydrogen  before  it  can  be  precipitated  as  a 
hydrate  in  Class  IV.  In  the  course  of  a  general  analysis 
no  precipitate  of  chromium  will  be  formed  unless  the  ele- 
ment is  present  as  a  salt  of  chromium,  or  has  been  reduced 
to  that  condition  by  the  action  of  the  sulphuretted  hydrogen 
used  to  precipitate  the  members  of  Classes  II  and  III. 


56  PBECIPITATES  OF  CLASS  IV,  [§  33. 

To  illustrate  this  point,  add  ammonia-water  to  a  solution 
of  chromate  of  potassium  —  acidulated  with  hydrochloric 
acid,  then  pass  sulphuretted  hydrogen  through  an  equal 
amount  of  the  chromate  of  potassium  acidulated  as  before, 
filter  if  necessary,  boil  the  filtrate  to  drive  off  excess  of 
sulphuretted  hydrogen  and  add  ammonia-water  in  excess 
as  before. 

It  will  be  remembered  that  the  object  of  using  chloride 
of  ammonium  is  to  hold  in  solution  magnesium  (of  Class 
VII)  and  the  members  of  Class  V.  This  it  does  in  virtue 
of  the  fact  that  the  double  salts  formed  by  the  union  of 
ammonium  compounds  with  compounds  of  the  elements  in 
question  are  soluble  in  water  and  also  in  ammonia-water. 
A  considerable  quantity  of  the  ammonium  salt  will,  of 
course,  be  formed  in  any  event  by  the  action  of  the  ammonia- 
water  upon  the  hydrochloric  acid  in  the  solution,  but  it  is 
best  always  to  add  a  further  portion  of  the  chloride  as  a 
precautionary  measure. 

-    The  following  inferences  may  be  drawn  from  the  color 
of  the  precipitate  produced  by  ammonia- water :  — 

A  gelatinous,  white  precipitate  indicates  aluminum  or 
some  one  of  the  oxalates,  phosphates,  etc.,  mentioned  above. 
In  this  case  test  at  once  for  phosphoric  and  oxalic  acids. 

A  grayish-green  or  grayish-blue  precipitate  indicates 
chromium. 

A  reddish-brown  precipitate  indicates  iron. 

If  no  precipitate  is  produced  by  the  ammonia-water,  all 
the  members  of  Class  IV  are  absent,  and  the  solution  may 
at  once  be  tested  with  sulphide  of  ammonium,  the  general 
reagent  of  Class  V. 

When  the  solution  contains  much  chromium,  a  small  por- 
tion of  this  element  is  apt  to  remain  dissolved  at  first  in 
the  excess  of  ammonia-water,  and  to  color  the  solution 
pink;  but  by  continuing  to  boil  the  solution,  the  color  may 
be  made  to  disappear,  and  the  whole  of  the  chromium  may 


§  33.]  ''MASHING''    OF  CLASS  IV.  57 

be  thrown  down.  Care  must  be  taken  to  replace,  by  small 
portions,  the  water  driven  off  by  boiling,  lest  some  of  the 
members  of  Class  Y  be  converted  into  insoluble  compounds. 
It  is  to  be  observed  that  the  legitimate  members  of  Class 
IV  cannot  be  completely  precipitated  by  ammonia-water 
from  solutions  which  contain  non-volatile  organic  substances, 
like  albumin,  sugar,  starch,  and  so  forth,  or  organic  acids 
(such  as  tartaric,  citric,  oxalic,  or  even  in  some  cases  acetic 
acid)  which  form  soluble  double  salts  by  uniting  simulta- 
neously with  the  ammonium  and  one  or  more  of  the  mem- 
bers of  the  class.  The  treatment  of  substances  containing 
organic  matter  will  be  explained  hereafter  (§  84). 


CHAPTER  VI. 

CLASS  v.  — ELEMENTS  WHOSE  SULPHIDES  ARE  INSOLU- 
BLE IN  WATER  AND  IN  SALINE  OR  ALKALINE  SOLU- 
TIONS. 

34.  Example   of  the   Precipitation  of  the  Members  of 

Class  V.  —  Place  in  a  small  glass  flask  a  lialf  teaspoonful  of 
aqueous  solutions  (App.,  §  66)  of  the  sulphates,  nitrates 
or  chlorides  of  cobalt,  nickel,  manganese  and  zinc.  Add  to 
the  mixture  six  or  seven  teaspoonfuls  of  a  solution  of 
chloride  of  ammonium,  as  much  water,  and  ammonia-water 
to  alkaline  reaction.  If  any  precipitate  appear  on  the 
addition  of  ammonia-water,  add  chloride  of  ammonium 
solution  and  warm  until  it  dissolves. 

Heat  the  mixture  to  boiling,  and  add  sulphide  of  am- 
monium to  the  boiling  solution,  drop  by  drop,  with  fre- 
quent agitation,  as  long  as  a  precipitate  continues  to  be 
formed.  (Compare  p.  13.)  In  the  present  case  there  are 
#  special  reasons  why  the  precipitate  should  be  boiled  and 
shaken,  in  order  to  make  it  compact ;  for  the  sulphides  of 
Class  V,  when  loose  and  flocculent,  are  not  only  easily  acted 
upon  by  the  air  and  by  dilute  acids,  but  are  peculiarly  liable 
to  pass  through  the  pores  of  filter  paper,  and  yield  muddy 
filtrates. 

At  the  best,  these  sulphides  oxidize  rapidly  when  moist, 
with  formation  of  soluble  sulphates  which  are  liable  to  pass 
through  the  filters  and  contaminate  the  filtrates.  The 
analysis  of  the  sulphides  should  therefore  be  proceeded 
with  immediately  after  the  precipitation  with  sulphide  of 

58 


§§  34,  35.]    ANALYSIS  OF  THE  MIXED  SULPHIDES.    59 

ammonium,  and  should  be  conducted  in  such  manner  that 
no  precipitate  of  a  sulphide  shall  ever  be  left  moist  upon  a 
filter  more  than  a  quarter  of  an  hour. 

35.  Analysis  of  the  Mixed  Sulphides.  —  The  detection  of 
the  several  members  of  Class  V  depends :  —  1st.  Upon  the 
almost  complete  insolubility  of  the  sulphides  of  cobalt  and 
nickel  in  cold  dilute  hydrochloric  acid,  and  the  ready  solu- 
bility of  the  sulphides  of  manganese  and  zinc  in  that  liquid. 
2d.  Upon  the  solubility  of  hydrate  of  zinc,  and  the  insolu- 
bility of  hydrate  of  manganese,  in  a  solution  of  sodium 
hydrate.  3d.  Upon  the  insolubility  of  sulphide  of  zinc 
in  acetic  acid,  in  presence  of  sulphuretted  hydrogen. 
4th.  Upon  the  peculiar  colors  imparted  to  borax  glass  by 
compounds  of  cobalt  and  nickel  dissolved  in  the  glass ;  and 
upon  certain  other  special  tests  to  be  described  directly. 

To  effect  the  separation :  —  Collect  the  precipitate  upon  a 
filter,  and  rinse  it  once  or  twice  with  water ;  spread  open 
the  filter  in  a  porcelain  dish,  and  cover  it  with  cold  dilute 
hydrochloric  acid.  Scarcely  any  of  the  sulphide  of  cobalt, 
or  of  nickel,  will  go  into  'solution,  while  the  sulphides 
of  manganese  and  zinc  will  be  completely  decomposed,  and 
dissolved  as  chlorides. 

Filter  the  hydrochloric  acid  solution,  pour  the  filtrate 
into  a  porcelain  dish,  and  boil  it  until  strips  of  moistened 
lead  paper  held  in  the  steam  no  longer  indicate  the  pres- 
ence of  sulphuretted  hydrogen;  then  add  sodium  hydrate 
to  the  liquid  in  slight  excess.  A  whitish  gelatinous  pre- 
cipitate of  hydrate  of  manganese,  which  turns  brown  on 
exposure  to  the  air  and  is  insoluble  in  sodium  hydrate,  will 
be  thrown  down,  together  with  small  portions  of  the 
hydrates  of  cobalt  and  nickel,  resulting  from  the  partial 
decomposition  of  the  sulphides  of  these  metals  by  the 
hydrochloric  acid,  while  the  hydrate  of  zinc  at  first  pre- 
cipitated redissoives  completely  in  the  excess  of  the  alka- 
line hydrate.     It  is  to  be  observed  that  precipitation  should 


60      SEPARATION  OF  MANGANESE  AND  ZINC.      [§  35. 

never  be  effected  in  a  porcelain  dish,  since  a  white  or 
transparent  precipitate  is  scarcely  visible  in  a  white  and 
opaque  dish. 

To  prove  the  presence  of  manganese,  collect  the  precipi- 
Test     tt'^te  upon  a  filter,  allow  it  to  drain,  and  fuse  a 
for       small  portion  of  it  with  a  mixture  of  carbonate  of 
^"-     sodium  and  nitrate  of  potassium  upon  platinum 
foil  in  the  oxidizing  blowpipe  flame,  as  directed  on  page  51. 
Divide  the  alkaline  filtrate  into  two  portions,  acidify  one 
portion  with  acetic  acid,  then  pass  sulphuretted  hydrogen 
Test     through   the    liquid.     Sulphide    of   zinc    will  be 
for      thrown  down  as  a  white  or  dirty  white  flocculent 
^^'     precipitate.      A  slight   decomposition  of   sulphu- 
retted hydrogen  whereby  sulphur  is  set  free,  may  give  a 
precipitate  liable  to  be  mistaken  for  sulphide  of  zinc;  but 
since  the  sulphide  is  soluble  in  hydrochloric  acid,  it  may 
be  distinguished  by  adding  a  small  quantity  of  this  reagent 
and  noting  whether  most  of  the  precipitate  dissolves.     Acid- 
ify the  other  portion  of  the  alkaline  filtrate  with  hydro- 
chloric acid.    Add  07ie  drop  of  a  solution  of  nitrate  of  cobalt, 
then  a  solution  of  carbonate  of  sodium  as  long  as  a  precipi- 
tate is  produced.     Boil  for  three   minutes,  filter,  dry  the 
filter  somewhat,  and  then  burn  either  on  platinum  foil  or 
on  charcoal.     In  the  presence  of  zinc  there  remains  an  ash 
of  a  peculiar  bluish-green  color.  y^ 

It  is  to  be  observed  that  in  the  analysis  of  mixtures 
which  contain  no  manganese  the  precipitate  of  hydrate  of 
cobalt  or  of  nickel  produced  by  the  sodium  hydrate  is  usu- 
ally small  and  sometimes  hardly  perceptible ;  but  no  matter 
how  minute  the  precipitate  may  be,  it  must  always  be  care- 
fully removed  by  filtration  before  testing  the  solution  for 
zinc  with  sulphuretted  hydrogen,  otherwise  the  white  pre- 
cipitate of  sulphide  of  zinc  will  be  obscured  by  the  black 
color  of  these  sulphides. 

The  black  residue,  insoluble  in  dilute  hydrochloric  acid, 
is  washed  with  water  and  tested  for  cobalt  and  nickel,  by 


§  35.]       SEPARATION  OF  COBALT  AND  NICKEL,         61 

heating  successive  small  portions  of  it  in  a  bead  (§  91,  e) 
of  borax  (App.,  §  '26)  in  tbe  oxidizing  blowpipe  xests 
flame.  If  cobalt  alone  were  present,  a  bright,  for 
pure  blue  color  would  be  imparted  to  the  bead.  Co&Ni. 
Ofi  the  other  hand,  if  the  precipitate  was  composed  solely 
of  sulphide  of  nickel,  the  borax  glass  would  assume 
a  peculiar  reddish-brown  color.  Mixtures  of  the  two  sul- 
phides yield  beads  of  various  tints,  according  to  the  pro- 
portions of  nickel  and  cobalt  contained  in  them.  By 
adding  the  precipitate  to  the  borax  by  repeated  small  por- 
tions, and  fusing  the  bead  anew  after  each  addition,  it  is 
often  possible  to  obtain  first  the  characteristic  color  of  one 
of  the  elements,  and  afterwards  tolerably  well  defined  indi- 
cations of  the  other. 

The  blue  color  of  cobalt  can  usually  be  made  manifest, 
even  in  presence  of  much  nickel,  by  heating  the  borax  bead 
in  the  reducing  blowpipe  flame  (App.,  §  82).  In  the  re- 
ducing flame  the  reddish-brown  color  imparted  by  nickel 
changes  to  gray,  while  the  cobalt  blue  remains  unaltered. 

In  any  event,  one  of  the  two  metals  will  be  detected  by 
the  blowpipe  test,  and  the  subsequent  operations  can  be 
limited  to  searching  for  the  other. 

To  prove  the  presence  of  nickel,  boil  the  black  residue 
with  a  few  drops  of  aqua  regia  in  the  porcelain  dish,  and 
evaporate  the  solution  almost,  but  not  quite,  to  dryness. 
Add  to  tJie  residual  acid  liquor,  little  by  little,  a  strong 
solution  of  cyanide  of  potassium,  until  the  reaction  of  the 
solution  becomes  decidedly  alkaline ;  the  cyanides  of  nickel 
and  cobalt  at  first  thrown  down  both  redissolve  easily  in 
an  excess  of  cyanide  of  potassium.  Boil  the  mixture  for 
several  minutes,  adding  water  by  small  portions  to  replace 
that  lost  by  evaporation.  Then  add  a  solution  of  hypo- 
chlorite of  sodium  until  the  liquid,  after  shaking,  smells 
strongly  of  it,  and  boil  again.  The  nickel  is  precipitated 
as  black  nickelic  hydrate  (NiH303),  while  the  compound 
of  cobalt  in  solution  (cobalticyanide  of  potassium)  is  not 


62  SEPABATION   OF  COBALT.  [§§  35, 36. 

affected.  If  a  light-colored  precipitate  appears,  it  may  indi- 
cate that  an  insufficient  quantity  of  hypochlorite  of  sodium 
has  been  added,  and  in  the  case  of  a  solution  actually  under 
examination  more  of  the  reagent  should  be  added  before 
pronouncing  nickel  absent.  The  alkaline  reaction  of  the 
liquid  must  be  maintained  by  the  addition  of  more  cyanide 
of  potassium,  if  necessary. 

To  confirm  the  presence  of  cobalt  in  case  of  doubt :  —  Dis- 
solve the  black  residue  in  a  few  drops  of  hot  aqua  regia, 
evaporate  the  solution  nearly  to  dryness,  pour  into  the 
residual  solution  two  or  three  times  its  own  volume  of  a 
solution  of  nitrite  of  potassium  (App.,  §  38),  and  add  to 
the  mixture  concentrated  acetic  acid,  until  the  reaction  of 

rpgg^  the  liquid  is  strongly  acid.  Transfer  the  mixture 
for       to  a  test-tube,  and  leave  it  at  rest  during  eighteen 

^°*  or  twenty -four  hours.  A  beautif-ul,  yellow  crystal- 
line precipitate  of  the  double  nitrite  of  cobalt  and  potassium 
will  be  deposited  sooner  or  later,  according  to  the  propor- 
tion of  cobalt  which  the  solution  contained. 

On  adding  sodium  hydrate  to  the  filtrate  from  the  cobalt 
precipitate,  hydrate  of  nickel  would  be  thrown  down  if 
present,  and  the  presence  of  nickel  might  be  confirmed  by 
testing  this  precipitate  with  borax  in  the  oxidizing  blow- 
pipe flame. 

36.  An  outline  of  the  foregoing  operations  may  be  tabu- 
lated as  follows :  — 


The  General  Reagent  [(NH4).^S]  of  Class  V  precipitates  CoS, 
NiS,  MnS   and  ZnS.     Treat  the  precipitate  with  dilute  HCl :  — 


CoS  and  NiS 
remain  undis- 
solved. 

Test  for  Co 
and  Ni  with 
borax  glass 
and,  if  need  be, 
with  NaClO  or 
KNO,. 


MnCI,  and  ZnCl.^  go  into  solution.     Boil,  to 
expel  HJS,  and  add  NaHO  :  — 


Hydrate  of  manganese  is 
precipitated,  together  with 
traces  of  the  liydrates  of 
Co  and  Ni. 

Prove  presence  of  Mn  by 
the  blowpipe  test. 


Hydrate  of  zinc 
goes  into  solution. 
Acidify  with  acetic 
acid,  and  add  H.^S 
to  throw  down 
ZnS. 


§  37.]        SEPARATION   OF  CLASSES  IV  AND   V.  63 

37.  Separation  of  Class  V  from  Class  IV.  After  Classes 
I,  II,  III  and  IV  have  been  removed  in  the  manner  already 
described  (§§9,  33),  add  a  single  drop  of  sulphide  of  ammo- 
nium of  good  quality  (App.,  §  18)  to  the  filtrate  from  Class 
IV.  If  no  precipitate  is  produced,  none  of  the  members  of 
Class  V  can  be  present,  and  the  solution  may  be  immedi- 
ately tested  with  carbonate  of  ammonium,  the  general  rea- 
gent of  Class  VI. 

If  the  first  drop  of  the  sulphide  produces  a  precipitate, 
transfer  the  mixture  to  a  small  flask,  heat  it  until  it  actu- 
ally boils,  and  add  more  of  the  sulphide,  with  the  precau- 
tions enjoined  on  page  13  to  complete  the  precipitation. 

In  case  the  precipitate  produced  by  sulphide  of  ammonium 
is  white,  the  presence  of  zinc  is  indicated. 

If  it  be  flesh-colored  or  yellowish-white  and  becomes 
brown  by  oxidation  when  exposed  to  the  air,  the  presence  of 
manganese  is  to  be  inferred. 

The  student  may  observe  these  changes  by  adding  some 
sulphide  of  ammonium  to  a  solution  of  manganese  chloride 
or  sulphate,  collecting  the  precipitate  on  a  filter  and  allow- 
ing it  to  stand  exposed  to  the  air  for  an  hour  or  two. 

In  case  the  precipitate  is  black,  either  cobalt  or  nickel, 
or  both  these  elements,  are  present.  Both  of  them  must 
be  sought  for,  whenever  the  precipitate  exhibits  any  tinge 
of  black  at  the  moment  of  its  formation. 

As  the  sulphide  of  nickel  is  not  absolutely  insoluble  in 
sulphide  of  ammonium,  it  not  infrequently  happens  that 
the  filtrate  from  Class  V  is  dark-colored,  owing  to  the  pres- 
ence of  sulphide  of  nickel  in  solution.  (If  it  has  a  deep 
brown  color,  nickel  may  be  safely  concluded  to  be  present.) 
In  such  case  it  is  well  to  acidify  the  liquid  with  hydro- 
chloric acid,  and  to  collect  the  dark-colored  precipitate 
(which  consists  of  sulphide  of  nickel  mixed  with  free  sul- 
phur) on  a  filter,  and  to  test  for  nickel  by  means  of  the 
borax  bead.  The  filtrate  must  then  be  made  alkaline  with 
ammonia-water  before  testing  for  Class  VI. 


64  SEPAttATION   OF  CLASSES  IV  AND   V.         [§  37. 

For'tlie  sake  of  illustration  the  student  may  add  an  excess 
of  sulphide  of  ammonium  to  a  few  drops  of  a  solution  of 
sulphate  or  nitrate  of  nickel  and  boil  for  a  few  minutes. 
Then  filter,  observe  the  color  of  the  filtrate,  and  add  dilute 
hydrochloric  acid  to  acid  reaction. 

To  illustrate  the  necessity  for  the  presence  of  chloride  of 
ammonium  to  prevent  the  precipitation  of  certain  members 
of  Class  V  with  the  hydrates  of  Class  IV,  the  following 
experiments  may  be  performed.  Take  ten  drops  of  solu- 
tions of  chloride  or  nitrate  of  cobalt,  dilute  with  water,  then 
add  ammonia- water  to  alkaline  reaction :  if  any  precipitate 
appear,  filter  and  to  the  clear  filtrate  add  sulphide  of 
ammonium.  Now  take  the  same  amount  of  cobalt  solu- 
tion as  before,  add  three  teaspoonfuls  of  chloride  of  am- 
monium solution,  then  add  ammonia-water  to  alkaline 
reaction. 


CHAPTER  VII. 

CLASS  VI.  —  ELEMENTS  WHOSE  CARBONATES  ARE  IN- 
SOLUBLE IN  WATER,  AMMONIA-WATER  AND  SALINE 
SOLUTIONS. 

38.  Example  of  the   Precipitation  of    the  Members  of 

Class  VI.  —  Place  in  a  small  beaker  a  teaspoonful  of  aque- 
ous solutions  of  the  chlorides  or  nitrates  of  barium,  stron- 
tium and  calcium.  Add  to  the  mixture  two  or  three 
teaspoonfuls  of  a  solution  of  chloride  of  ammonium,  enough 
ammonia-water  to  produce  an  alkaline  reaction,  and  finally 
a  solution  of  carbonate  of  ammonium,  drop  by  drop,  as  long 
as  any  precipitate  continues  to  be  produced  by  fresh  por- 
tions of  this  reagent.  To  determine  this  last  point,  heat 
the  mixture  to  boiling  at  intervals,  and  after  boiling  allow 
it  to  settle  until  a  sufficient  quantity  of  comparatively  clear 
liquid  has  collected  at  the  top  of  the  mixture  to  permit  the 
application  of  the  test. 

39.  Analysis  of  the  Mixed  Carbonates.  —  The  separation 
of  barium,  strontium  and  calcium,  one  from  the  other, 
depends :  —  1st.  Upon  the  insolubility  of  chromate  of  barium 
in  dilute  acetic  acid,  and  the  solubility  of  the  chromates 
of  strontium  and  calcium  in  that  liquid.  2d.  Upon  the 
fact  that  sulphate  of  strontium  is  almost  absolutely  insolu- 
ble in  acidulated  water,  while  sulphate  of  calcium,  though 
rather  sparingly  soluble  in  water,  is  still  sufficiently  soluble 
to  be  kept  in  solution.     (See  App.,  §  31.) 

Collect  the  precipitate  upon  a  filter,  wash  it  two  or  three 
times  with  water,  taking  care  to  collect  the  precipitate  at 
the  apex  of  the  filter,  and  dissolve  it  in  acetic  acid.     The 

65 


66  SEPARATION   OF  BARIUM.  [§  30. 

acid  may  be  poured  into  the  filter  as  it  rests  in  the  funnel, 
but  only  a  few  drops  should  be  used,  and  the  filtrate  should 
be  poured  back  repeatedly  upon  the  filter,  until  all  the  pre- 
cipitate has  been  dissolved.  If  the  portion  of  acid  at  first 
taken  becomes  saturated  before  the  precipitate  is  entirely 
dissolved,  it  will  be  necessary  to  add  an  additional  small 
amount.  Finally  rinse  the  filter  with  a  little  water  from 
a  wash-bottle  with  small  orifice,  collect  the  wash-water 
with  the  filtrate,  and  shake  the  mixture. 

Pour  a  small  portion  of  the  acetic  acid  solution  into  a 

test-tube,   and  add  to  it  a  drop  of  a    solution  of   normal 

chromate  of  potassium.     A  pale  yellow    precipitate    falls 

when  barium  is  present,  as  in  this  instance;  for  chromate 

Test      of   barium  is  well-nigh   insoluble  in  acetic   acid, 

for       especially    in   presence    of    saline   solutions.     In 

^^_:      order  to  separate  the  whole  of  the  barium,  pour 


the  contents  of  the  test-tube  into  the  reserved  portion  of 
the  acetic  acid  solution,  heat  the  mixture  to  boiling,  and 
add  to  it  chromate  of  potassium,  until  no  more  precipitate 
falls  and  the  supernatant  liquor  appears  distinctly  yellow, 
after  having  been  well  shaken  and  allowed  to  settle.  Filter 
the  mixture,  and  proceed  to  examine  the  filtrate  for  stron- 
tium and  calcium. 

If  no  barium  had  been  present,  no  precipitate  would  have 
been  produced  by  chromate  of  potassium  in  the  small  por- 
tion of  liquid  first  tested,  and  it  would  have  been  unneces- 
sary to  mix  this  reagent  with  the  rest  of  the  acetic  acid 
solution.  Trouble  would  thus  be  saved,  as  will  appear 
below. 

It  sometimes  happens  that  chromate  of  barium  is  precipi- 
tated in  the  form  of  powder  so  fine  that  some  particles  of 
it  pass  through  the  pores  of  the  paper  and  contaminate  the 
filtrate.  Now,  in  order  to  detect  strontium  and  calcium  it 
is  absolutely  necessary  that  this  filtrate,  although  of  a 
bright  yellow  color,   should  be  perfectly  transparent  and 


§  39.]  SEPARATION  OF  STRONTIUM  AND  CALCIUM.      67 

free  from  suspended  particles  of  the  barium  salt.  If  then 
the  filtrate  is  at  all  turbid,  it  must  be  poured  back  re- 
peatedly into  the  filter,  and  again  collected  in  clean  tubes, 
until  the  last  trace  of  cloudiness  has 'disappeared. 

To  the  filtrate  from  the  chromate  of  barium  add  ammo- 
nia-water to  alkaline  reaction,  and  carbonate  of  ammonium 
as  long  as  a  precipitate  falls.  Heat  the  mixture  to  boiling 
for  a  moment,  collect  the  precipitate  upon  a  small  filter, 
and  wash  it  with  water,  until  all  the  chromate  of  potas- 
sium has  been  removed,  and  the  wash-water  runs  colorless 
from  the  filter. 

Dissolve  the  precipitate  in  the  smallest  possible  quantity  j 
of  acetic  acid,   and  mix  it  with  three   or   four   times   its 
volume  of  a  solution  of  sulphate  of  potassium  (App.,  §  31), 
made  of  such  strength  that,  though  capable  of  throwing 
down  sulphate  of  strontium,  it  cannot  precipitate  sulphate 
of  calcium.     Allow  the  mixture  to  stand  at  rest  for  two 
hours  or  more,  in  order  that  the  white  powder  of  sulphate 
of    strontium    may   separate    completely.     Then      Tests 
filter,  and  to  the   filtrate  add  ammonia- water  to       for 
\y   alkaline    reaction,    and   half   a  teaspoonful   of  a  Sr  &  Ca. 
solution  of  oxalate  of  ammonium.     A  white  precipitate  of 
oxalate  of  calcium  will  be  immediately  thrown  down. 

Since  sulphate  of  strontium  is  somewhat  soluble  in  a  solu- 
tion of  chromate  of  potassium,  the  filtrate  from  chromate 
of  barium  cannot  be  examined  directly  for  strontium  by 
means  of  sulphate  of  potassium.  The  strontium  and  cal- 
cium are  consequently  reprecipitated  as  carbonates,  in  order 
that  the  excess  of  chromate  of  potassium  may  be  washed 
away.  The  operation  serves  also  to  collect  the  strontium 
and  calcium  out  of  the  mass  of  liquid  in  which  they  have 
become  diffused,  and  to  concentrate  them  to  a  small  bulk. 

It  should  be  observed  that,  when  the  proportion  of 
strontium  or  calcium  in  a  mixture  is  small,  it  often  hap- 
pens that  the  precipitate,  produced  by  carbonate  of  ammo- 


68 


SEPARATION  OF  CLASS   VL 


[§§  39-41. 


nium  in  the  filtrate  from  chromate  of  barium,  is  held  in 
suspension  and  concealed  so  completely  in  the  yellow- 
liquor,  that  an  unpractised  eye  can  hardly  detect  the  fact 
that  the  liquid  ha'fe  become  cloudy.  That  a  precipitate  has 
really  been  formed  in  such  cases  is  easily  discovered  by 
throwing  a  portion  of  the  mixture  upon  a  filter,  and  com- 
paring the  clear  filtrate  thus  obtained  with  that  portion 
of  the  mixture  which  has  been  left  unfiltered. 

40.  An  outline  of  the  foregoing  operations  may  be  pre- 
sented in  tabulaT  form  as  follows :  — 


The  General  Reagent,  [NH4J2C03,  of  Class  VI  precipitates  the 
carbonates  of  Ba,  Sr  and  Ca.  Dissolve  in  dilute  acetic  acid,  and 
add  K^CrO^ :  — 


BaCrOi 

is   thrown 
down  as 
a  yellow 
powder. 


Sr  and  Ca  remain  in  solution.    Add  (NHJHO  and 

(NH4)2C03.   Collect  and  wash  the  precipitate,  and  dis- 
solve it  in  acetic  acid.    Add  dilute  K^SO^ :  — 


SrSO, 

is  thrown 
down. 


Ca  remains  in  solution.    Add  oxalate  of 
ammonium,  to  precipitate  the  calcium  as 

oxalate. 


i^'t- 


41.   Separation  of  Class  VI  from  the  Preceding  Classes.  — 

After  Classes  I,  II,  III,  IV  and  V  have  been  separated  in 
the  manner  already  described  (§§  6  to  10),  there  will  still 
always  remain  to  be  examined  the  filtrate  from  Class  V, 
and  sometimes  a  precipitate  (§  31)  composed  of  oxalates  of 
barium,  strontium,  calcium  (and  magnesium),  —  in  case 
any  salt  of  these  elements,  insoluble  in  ammonia-water, 
has  been  thrown  down  with  the  members  of  Class  IV. 

If  such  a  precipitate  has  been  obtained  in  the  analysis  of 
Class  IV,  the  oxalic  acid  contained  in  it  must  now  be 
destroyed,  the  remainder  of  the  precipitate  brought  into 
solution,  and  this  solution  added  to  the  filtrate  from  Class 

V,  before  proceeding  to  precipitate  the  members  of  Class 

VI.  To  this  end,  ignite  the  dry  precipitate  carefully  upon 
platinum  foil,  —  by  several  successive  portions  if  the  pre- 


§  41.]  SEPARATION   OF  CLASS    VL  69 

cipitate  is  large,  —  taking  care  that  none  of  the  powder  is 
left  sticking  to  the  paper  or  lost  by  dropping  it  from  the 
foil.  At  a  moderate  heat  the  oxalates  suifer  decomposi- 
tion, and  only  carbonates  or  oxides  are  left  upon  the  foil. 
Place  the  foil  and  the  residue  in  a  small  porcelain  dish, 
and  dissolve  the  residue  in  boiling  dilute  hydrochloric  acid. 
Add  a  few  drops  of  chloride  of  ammonium  to  the  solution, 
neutralize  the  acid  with  ammonia-water,  pour  the  liquid 
upon  a  small  filter,  and  add  the  filtrate  to  that  obtained 
from  Class  V.  Then  add  a  solution  of  carbonate  of  am- 
monium to  the  mixture,  and  boil  it  in  the  manner  described 
in  §  38. 

If  there  be  no  precipitate  of  the  oxalates  from  Class  TV, 
the  filtrate  from  Class  V  will,  of  course,  be  treated  directly 
with  carbonate  of  ammonium,  care  being  taken  to  add  only 
a  drop  or  two  of  the  reagent,  at  first,  to  ascertain  whether 
any  of  the  members  of  Class  VI  are  really  contained  in 
the  solution. 

The  solution  to  which  the  general  reagent  carbonate  of 
ammonium  is  added  must  contain  chloride  of  ammonium, 
to  prevent  the  precipitation  of  magnesium  as  a  carbonate, 
and  also  ammonia-water,  to  hinder  the  decomposition  of  the 
carbonates  of  barium,  strontium  and  calcium  by  the  boiling 
chloride  of  ammonium.  But  since  the  excess  of  ammonia- , 
water  and  the  chloride  of  ammonium,  added  to  the  solution 
before  the  separation  of  Class  IV,  are  still  contained  in  it, 
no  new  quantity  of  either  of  them  need  here  be  added. 

One  difficulty  inherent  to  this  method  of  analysis  is  that 
the  carbonates  of  barium,  strontium  and  calcium  are  all 
slightly  soluble  in  a  solution  of  chloride  of  ammonium. 
This  fact  can  readily  be  exhibited  by  adding  a  teaspoonful 
of  oxalate  of  ammonium  solution  to  the  filtrate  from  the 
precipitate  of  mixed  carbonates  (§  39)  and  allowing  the 
mixture  to  stand  for  some  time.  A  white  precipitate  of 
oxalate  of  barium,  strontium  or  calcium  will  fall,  because 


70  SEPARATION   OF  CLASS   VI.  [§  41. 

the  oxalates  of  these  metals  are  less  readily  soluble  than 
the  carbonates  in  a  solution  of  ammonium  chloride.  This 
solubility  of  the  carbonates  is  so  marked  that  no  precipitate 
whatever  is  produced,  when  carbonate  of  ammonium  is 
added  to  a  weak  solution  of  either  of  the  members  of  Class 
VI,  in  case  a  large  quantity  of  chloride  of  ammonium  has 
been  previously  mixed  with  it.  On  this  account  it  is  well 
in  an  actual  analysis  to  concentrate  by  evaporation  the 
filtrate  from  the  Class  V  precipitate  before  adding  the 
carbonate  of  ammonium  solution,  and  in  some  cases,  where 
a  very  large  amount  of  ammonium  salts  is  present,  it  is 
well  to  evaporate  to  complete  dryness  and  then  to  ignite  in 
order  to  drive  off  the  ammonium  compounds.  The  residue 
when  cold  is  dissolved  in  a  small  quantity  of  hydrochloric 
acid ;  two  or  three  teaspoonfuls  of  a  solution  of  chloride  of 
ammonium  are  added,  then  ammonia-water,  and,  finally, 
carbonate  of  ammonium,  as  in  §  38. 

In  a  solution  containing  traces  of  barium  or  strontium 
these  elements  might  fail  to  be  detected,  in  case  the  hydro- 
chloric acid  employed  in  the  process  of  separating  Classes  I 
and  II  was  contaminated  with  sulphuric  acid,  or  in  case  the 
original  liquid  contained  nitric  acid  to  oxidize  a  portion  of 
the  sulphur  of  the  sulphuretted  hydrogen  employed  to  pre- 
cipitate Class  II  and  Class  III,  or  even  if  the  nitric  acid, 
employed  to  oxidize  iron  in  the  filtrate  from  Classes  II  and 
III,  were  added  before  the  sulphuretted  hydrogen  had  been 
expelled,  or  if  a  powerful  oxidizing  agent  was  present  in 
the  solution  through  which  sulphuretted  hydrogen  was 
passed.  Almost  all  danger  is  avoided,  however,  by  using 
pure  hydrochloric  acid  to  precipitate  Class  I,  and  expelling 
the  nitric  acid  from  the  filtrate  by  evaporating  the  latter 
to  dryness  at  a  gentle  heat,  covering  the  residue  with  pure 
concentrated  hydrochloric  acid,  again  evaporating  to  dry- 
ness, and  finally  dissolving  in  water  acidulated  with  hydro- 
chloric acid. 


•     CHAPTER  VIII. 


CLASS  VII.  —  INCLUDES  THE  REMAINING  COMMON  ELE- 
MENTS NOT  COMPRISED  IN  THE  PRECEDING  CLASSES, 
NAMELY:   MAGNESIUM.   SODIUM  AND  POTASSIUM. 

42.  The  Detection  of  the  Several  Members  of  Class  VII 

depends:  —  1st.  Upon  the  insolubility  of  a  double  phos- 
phate of  magnesium  and  ammonium,  and  the  solubility  of 
the  phosphates  of  x^otassium  and  of  sodium ;  and  2d.  Upon 
the  fact  that  compounds  of  sodium  and  potassium  impart 
peculiar  colorations  to  non-luminous  flames,  like  those  of 
alcohol  and  of  a  mixture  of  coal-gas  and  air. 

Prepare  a  mixture  of  a  small  teaspoonful  of  solutions 
(App.,  §  66)  of  almost  any  one  of  the  salts  of  magnesium, 
sodium  and  potassium,  and  add  to  the  mixture  an  equal 
bulk  of  chloride  of  ammonium.  Pour  a  quarter  of  the 
mixture  into  a  test-tube  and  the  remainder  into  a  small 
porcelain  dish.  Add  to  the  contents  of  the  test-tube  two 
or  three  drops  of  a  solution  of  phosphate  of  sodium,  and 
as  much  ammonia-water,  and  shake  the  cold  mixture  at 
frequent  intervals.  A  crystalline,  white  precipi-  Test 
tate  of  the  double  phosphate  of  magnesium  and  for 
ammonium  will  appear  after  a  longer  or  shorter      ^S- 


interval,  according  as  the  original  solution  was  more  or  less 
dilute. 

43.  Evaporate  the  contents  of  the  porcelain  dish  to  dry- 
ness, ignite  the  residue  until  the  chloride  of  ammonium  has 
been  completely  expelled,  —  a  point  which  will  be  indi- 
cated by  the  cessation  of  fuming,  —  allow  the  dish  to  cool, 
and  pour  into  it  three  or  four  drops  of  water. 

Carefully  clean  the  loop  on  a  piece  of  platinum  wire  by 

71 


72      SEPARATION  OF  SODIUM  AND  POTASSIUM.    [§  43. 

washing  it  repeatedly  with  water,  and  finally  holding  it  in 
the  lamp  flame  until  the  last  traces  of  sodium  compounds 
Test     ^1*6  burned  off,  and  it  ceases  to  color  the  flame, 
for       Without  touching  the  loop  with*the  fingers,  dip 
^*-      it  into  the  aqueous  solution  in  the  dish,  and  again 
hold  it  in  the  flame.     A  bright  yellow  color  will  be  im- 
parted to  the  flame  by  the  sodium  contained  in  the  mixture ; 
but  the  color  peculiar  to  potassium  compounds  will  be  invis- 
ible, since  the  yellow  color  of  the "  sodium  overpowers  and 
conceals  it.     Dip  the  loop  a  second  time  in  the  solution, 
and  again  hold  it  in  the  lamp  flame ;  but  this  time  look  at 
the  flame  through  a  piece  of  deep-blue  cobalt  glass.     This 
cobalt  glass  is  the  ordinary  blue  glass  used  for  stained 
glass  windows;  it  is  essential  that  the  glass  should  be  of 
moderate    thickness,    and   colored    blue    throughout,    not 
simply   *' flashed"    with  blue.      The   characteristic  violet 
Test     color  imparted  to  a  flame  by  potassium  compounds 
for      will  now  be  visible,  for  the  blue  glass  shuts  off 
^'       completely  the  yellow  sodium  light,  while  it  per- 
mits the  free  passage  of  the  violet  rays.  • 

Since  traces  of  compounds  of  sodium  and  potassium  are 
to  be  found  almost  everywhere,  it  is  sometimes  difficult  to 
determine  by  the  foregoing  tests  whether  the  substance 
under  examination  contains  one  or  the  other  of  these  ele- 
ments as  an  essential  ingredient,  or  merely  as  an  accidental 
impurity.  It  is  always  possible,  however,  to  separate  the 
sodium  or  the  potassium  from  the  other  members  of  the 
class,  and  to  decide,  by  actual  inspection  of  the  isolated 
compounds,  whether  one  or  both  of  these  substances  is  con- 
tained in  really  appreciable  quantity  in  the  substance  sub- 
jected to  analysis.  To  this  end  evaporate  the  aqueous 
solution  last  mentioned  which  contains  the  chlorides  of 
magnesium,  of  sodium  and  of  potassium,  almost  to  dryness, 
mix  thoroughly  with  the  evaporated  solution  an  equal  bulk 
of  red  oxide  of  mercury  (App.,  §  54),  and  ignite  the  mixture 


§§  43,44.]  ISOLATION   OF  CLASS   VIL  73 

until  all  fuming  ceases.  The  chloride  of  magnesium  will 
be  changed  to  oxide,  while  the  easily  volatile  chloride  of 
mercury  escapes. 

MgCl2  +  HgO  =  HgCl2  +  MgO. 

The  ignition  should  be  effected  beneath  a  chimney  or  in  a 
draught  of  air  powerful  enough  to  carry  away  the  poison- 
ous fumes  of  the  corrosive  sublimate.    Boil  the  residue  after 
ignition  with  a  small  quantity  of  water ;  separate  the  insolu- 
ble oxide  of  magnesium  together  with  the  excess  of  oxide 
of  mercury  by  filtration.     Evaporate  the  filtrate  to  a  small 
bulk  with  addition  of  two  or  three  drops  of  hydrochloric 
acid  and  a  half  a  teaspoonful  of  a   solution  of  platinic 
chloride  (App.,  §  56).     A  yellow  crystalline  precipitate  of 
chloroplatinate  of  potassium  will  separate  either  at  once  or 
after  some  time.    In  order  to  hasten  the  precipita-     xest 
tion  of  the  potassium  compound,  which  is  some-      for 
what  less  soluble  in  the  presence  of  alcohol  than      ^• 
in  water  alone,  evaporate  the  solution  to  which  the  platinic 
chloride  has  been  added  to  a  small  bulk;  disregarding  any 
precipitate  "whigh  may  form,  transfer  to  a  test-tube  and  add 
to  the  solution,  which  should  be  yellow  in  color,  or  more 
platinic  chloride  must  be  added,  an  equal  volume  of  alcohol ; 
sha^   and  let  stand  for   fifteen  minutes.     Separate    the 
chloroplatinate  of   potassium  by  filtration,  and  allow  the 
alcoholic  filtrate,  which  should  of  course  still  have  a  yellow 
color,  showing  that  excess  of  platinic  chloride  has      Test 
been  added,  to  evaporate  spontaneously  in  a  watch-      for 
glass.     Characteristic  crystals  of   chloroplatinate      ^^* 
of  sodium  will  be  seen  in  the  form  of  long,  slender  prisms 
or  needles  of  a  yellow  color. 

44.  The  Isolation  of  Class  VII,  by  the  removal  of  the 
preceding  classes,  has  been  described  in  §  12.  Care  must 
always  be  taken  to  concentrate  the  whole  of  the  filtrate 
from  Class  VI  by  evaporation,  before  testing  a  portion  of 


74:  SEPARATION   OF  CLASSES.  [§§  44,  45. 

it  for  magnesium;  and  time  enough  must  be  allowed  for 
the  magnesium  precipitate  to  crystallize ;  from  very  dilute 
solutions  it  may  not  separate  for  twenty-four  hours.  A 
slight  flocculent  precipitate  is  often  obtained  on  the  addi- 
tion of  the  phosphate  of  sodium  to  test  for  magnesium 
due  sometimes  to  the  presence  of  aluminum,  forming  phos- 
phate of  aluminum,  from  the  use  of  too  large  an  excess  of 
ammonium  hydrate  in  Class  IV ;  sometimes  to  the  imper- 
fect precipitation  of  barium,  strontium  or  calcium  as  car- 
bonates in  the  presence  of  much  ammonium  chloride  or 
alkaline  chlorides.  The  crystalline  character  of  the  mag- 
nesium compound  serves  to  distinguish  it,  and  can  usually 
be  detected  without  difficulty  from  the  manner  in  which 
it  forms  on  the  sides  of  the  test-tube,  if  rubbed  with  a  glass 
rod,  or,  if  necessary,  by  using  a  microscope. 

The  remainder  of  the  filtrate  from  Class  VI  must  be 
evaporated  to  dryness  and  ignited  until  all  fuming  ceases, 
before  testing  for  potassium  and  sodium,  in  order  that  the 
flame  reactions  of  those  elemems  may  not  be  concealed  or 
obscured  by  the  vapors  of  ammonium  salts  or  by  the  com- 
bustion of  particles  of  organic  matter  dei^ived  from  the 
various  reagents  which  have  been  added  in  the  course  of  the 
analysis,  and  also  because  chloride  of  ammonium  forms  with 
platinic  chloride  a  chloroplatinate  of  ammonium  similar  in 
appearance  and  insolubility  to  the  potassium  compound. 
In  order  to  apply  the  chloroplatinate  tests  for  sodium  and 
potassium,  it  is  necessary  that  they  should  be  present  in  the 
solution  in  the  form  of  chlorides.  The  iodides  of  these 
elements  react  with  platinic  chloride  to  form  black  platinic 
iodides,  coloring  the  solution  brownish-red  in  excess  of  the 
reagents. 

45.  An  outline  of  the  methods  employed  for  separating 
the  several  classes  is  here  presented  in  tabular  form.  The 
precautions  necessary  in  the  consecutive  examination  of  an 
"  unknown  "  solution  for  the  members  of  the  various  classes 
have  been  already  given  under  the  several  classes. 


§  45.] 


SEPARATION  OF  CLASSES. 


75 


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CHAPTER  IX. 

IRAL  TESTS  FOR  THE  NON-METALLIC  ELEMENTS. 

46.  The  following  common  elements  remain  to  be  con- 
sidered :  —  Sulphur,  nitrogen,  phosphorus,  carbon,  boron, 
silicon,  chlorine,  bromine,  iodine,  fluorine,  oxygen,  hydro- 
gen. It  is  obvious  that  oxygen  and  hydrogen  cannot  be 
directly  sought  for  by  any  analytical  process  conducted  in 
the  wet  way.  These  elements  are  added  to  the  original 
matter  in  the  water  or  acid  which  is  used  as  a  solvent. 
The  presence  of  these  elements  is  either  inferred  from  the 
other  results  of  the  analysis,  or  forms  the  object  of  direct 
inquiry  in  the  preliminary  treatment,  —  that  important  part 
of  every  analysis  which  forms  the  main  subject  of  Part  II. 
The  remaining  elements  all  belong  to  that  class  vaguely 
described  as  non-metallic;  they  unite  with  oxygen,  hydro- 
gen, or  both  these  elements,  to  form  what  are  commonly 
called  adds. 

As  the  metallic  elements  are  recognized  through  familiar 
compounds,  hydrates,  chlorides,  sulphides,  or  other,  so 
these  non-metallic  elements  are  identified  by  working  out 
of  the  unknown  mixture  their  characteristic  compounds. 
These  compounds  are  generally  salts.  But  there  is  one 
marked  difference  between  the  search  for  the  metallic  and 
the  search  for  the  non-metallic  elements  in  the  wet  way. 
In  the  case  of  iron  and  mercury  it  is  commonly  necessary 
to  determine  whether  the  element,  if  present,  exists  as  a 
ferrous  or  ferric,  as  a  mercurous  or  mercuric  salt,  in  the 
case  of  chromium  whether  as  a  chromate  or  a  salt  of  chro- 
mium; but  as  a  rule  it  is  true  that  no  question  usually 
76 


§  46.]  CLASSES   OF  SALTS,  77 

arises  in  connection  with  the  determination  of  a  metallic 
element,  except  the  fundamental  one  of  its  presence  or 
absence  in  a  given  solution.  The  sodium  in  the  three 
different  salts,  sulphate,  sulphite  and  hyposulphite  of 
sodium,  for  example,  is  detected  by  one  and  the  same 
method;  but,  when  the  other  elements  of  these  salts  9jjj^l 
sought  for,  three  different  reactions  will  occur,  accordin^^^' 
the  varying  nature  of  the  ingredients  other  than  sodium. 
A  sulphate  in  solution  gives  one  set  of  reactions,  a  sulphite 
another,  and  a  hyposulphite  a  third.  It  is  important  to 
do  more  than  determine  the  mere  presence  of  sulphur  and 
oxygen.  We  want  to  know  whether  the  sodium  salt  be  a 
sulphate,  sulphite  or  hyposulphite.  Analogous  questions 
arise  with  regard  to  other  non-metallic  elements;  there  is 
chlorine  both  in  chlorides  and  chlorates,  and  carbon  both  in 
carbonates  and  oxalates.  Arsenic,  too,  may  be  present  in 
the  form  of  arsenite  or  arseniate,  and  these  two  different 
kinds  of  salts  exhibit  many  quite  dissimilar  reactions. 

In  the  systematic  analysis  of  an  unknown  substance,  the 
examination  for  the  metallic  elements  by  the  methods 
detailed  in  the  previous  chapter,  as  a  ruUy  precedes  the 
determination  of  the  non-metallic  elements.  Having  ascer- 
tained which  of  the  metallic  elements  are  present  in  the 
substance  under  examination,  the  analyst  tries  to  identify 
each  class  of  salts  which  may  be  present  by  precipitating, 
or  otherwise  making  manifest,  some  familiar  member  of 
that  class.  Thus  he  identifies  sulphates  by  precipitating 
sulphate  of  barium,  chlorides  by  precipitating  chloride  of 
silver,  carbonates  by  throwing  down  carbonate  of  calcium, 
and  so  forth.  The  practically  important  inquiry  is,  how  to 
find  means  of  identifying  each  of  the  principal  classes  or 
kinds  of  salts.  The  word  "class"  or  "kind"  of  salts  is 
used  in  this  connection  as  a  collective  name  for  all  the 
salts  which  may  be  regarded  as  derived  from  one  and  the 
same  a,cid;  thus  all  sulphates  constitute  one  class  or  kind, 


78       TESTING  FOE  NON-METALLIC  ELEMENTS.     [§  46. 

all  carbonates  another,  and  so  forth.  The  following  com- 
mon classes  of  salts  are  those  for  which  more  or  less  per- 
fect means  of  recognition  will  be  given  in  this  chapter :  — 
Sulphates,  sulphites,  hyposulphites,  sulphides,  arseniates, 
arsenites,   phosphates,   carbonates,   oxalates,  tartrates,  bo- 

es,  silicates,  chromates,  fluorides,  chlorides,  bromides, 
des,  cyanides,  nitrates,  chlorates,  acetates. 

No  system  of  successive  testing  and  elimination,  analo- 
gous to  that  already  described  for  the  metallic  elements,  has 
been  devised  for  the  non-metallic  constituents  of  salts. 
There  are,  indeed,  certain  so-called  general  reagents  for 
adds;  but  these  reagents  are  chiefly  useful  to  show  the 
simultaneous  presence  or  absence  of  members  of  several 
classes  of  salts,  and  hardly  help  towards  the  identification  of 
any  individual  class,  except  in  cases  of  the  simplest  sort, 
in  which  only  a  single  class  of  salts  is  represented. 

It  sometimes  happens  that  the  preliminary  examination 
(§§  82,  83)  of  the  substance  to  be  analyzed  leads  directly  to 
some  conclusion  as  to  the  class  of  salts  in  hand.  A  knowl- 
edge of  the  metallic  element  or  elements  present  is  more- 
over in  most  cases  a  great  help  in  the  determination  of  the 
other  constituents.  It  is  for  this  reason  that  the  search 
for  the  metallic  elements  precedes  the  examination  for  the 
non-metallic.  A  single  example  will  sufficiently  illustrate, 
for  the  present,  this  important  principle,  which  is  of  very 
wide  application  in  qualitative  analysis. 

Suppose  that  the  substance  under  examination  is  a  solid 
which  dissolves  without  difficulty  in  water  and  which 
proves  to  contain  barium.  From  the  presence  of  barium 
in  a  compound  soluble  in  water,  it  is  to  be  directly  inferred 
that  there  is  no  sulphate,  phosphate,  carbonate,  oxalate  or 
tartrate  in  the  original  substance  since  these  barium  salts  are 
insoluble  in  water.  The  list  of  salts  excluded  by  the  demon- 
strated presence  of  barium  would  be  very  long.  So  it  is  in 
greater  or  less  degree  with  many  other  metallic  elements. 


|§  46,  47.]  THE  BARIUM  TEST.  79 

It  is,  indeed,  no  easy  matter  to  make  a  solution  containing 
even  one  representative  of  the  seven  classes  into  whicli  the 
metallic  elements  have  been  divided,  because  each  of  these 
elements,  except  sodium  and  potassium,  when  present  in 
a  solution,  excludes  one  or  more  whole  classes  of  salts.  By 
attending  to  just  inferences  to  be  drawn  from  the  quality 
of  the  metallic  elements,  much  time  will  be  saved,  and  the 
want  of  a  systematic  procedure  in  searching  for  the  non- 
metallic  elements  will  be  little  felt.  The  presence  of  the 
arsenites  and  arseniates,  of  carbonates,  chromates,  cyanides, 
sulphides,  sulphites  and  hyposulphites  will  ordinarily  be 
revealed  in  the  course  of  the  search  for  the  metallic 
elements. 

Before  giving  the  special  tests  by  which  the  above-men- 
tioned classes  of  salts  are  identified,  we  proceed  to  describe 
certain  general  tests  which  are  of  value,  particularly  when 
they  give  negative  results. 

47.  The  Barium  Test.  —  When  a  solution  of  chloride  (or 
nitrate)  of  barium  is  added  in  suitable  quantity  to  a  neutral 
or  slightly  alkaline  solution  containing  representatives  of 
any  or  all  of  the  following  classes  of  salts,  precipitation 
"usually  occurs,  for  all  these  salts  of  barium  are  insoluble  in 
water  and  alkaline  liquids,  if  no  ammonium  salts  be  pres- 
ent :  — 

Sulphates,  Phosphates,  Silicates, 

Sulphites,  Carbonates,  Chromates, 

Hyposulphites,  Oxalates,  Fluorides. 

Arseniates,  Tartrates, 

Arsenites,  Borates, 

If  the  chloride  (or  nitrate)  of  barium  fail  to  produce  a 
precipitate  under  the  prescribed  conditions,  the  complete 
absence  of  all  the  above  thirteen  classes  of  salts  is  at  once 
demonstrated,  provided  that  no  ammonium  salts  be  con- 
tained in  the  original  solution. 


80  THE  BARIUM  TEST,  [§§  48, 49. 

48.  Illustration  of  the  Barium  Test.  —  Prepare  in  a  test- 
tube  a  solution  containing  at  once  sulphate,  phosphate  and 
carbonate  of  sodium ;  a  very  small  bit  of  each  salt  will  be 
sufficient.  The  solution  will  be  found  to  be  alkaline  to 
litmus  paper.  Add  to  it  chloride  of  barium  (App.,  §  44), 
little  by  little,  until  a  fresh  addition  of  the  reagent  no 
longer  produces  an  additional  precipitate.  The  white  pre- 
cipitate consists  of  sulphate,  phosphate  and  carbonate  of 
barium.  All  the  thirteen  barium  salts  which  are  liable  to 
precipitation  under  these  circumstances  are  white,  with  the 
single  exception  of  chromate  of  barium.  The  yellow  color 
of  the  chromate  of  barium  (§  39)  distinguishes  this  one 
precipitate  from  all  the  rest.  If  this  color  is  well  marked, 
the  presence  of  a  chromate  in  the  original  solution  (which 
must  also  have  been  yellow)  may  be  inferred  with  cer- 
tainty. In  all  other  cases,  however,  the  precipitate  is 
white,  as  in  the  present  experiment.  The  next  question 
is,  can  anything  further  be  learned  from  this  white  precipi- 
tate? 

Add  to  the  contents  of  the  test-tube  dilute  hydrochloric 
acid,  until  the  liquid  has  a  decidedly  acid  reaction  to  lit- 
mus paper.  An  effervescence  indicates  the  escape  of  car- 
bonic acid,  displaced  by  the  less  volatile  hydrochloric  acid. 
The  bulky  precipitate  which  the  chloride  of  barium  pro- 
duced will  in  part  disappear,  but  a  portion  of  it  remains 
undissolved.  Filter  the  contents  of  the  tube.  The  parti- 
cles of  precipitated  sulphate  of  barium  are  so  very  fine  that 
they  often  pass  through  the  pores  of  the  paper,  necessitat- 
ing repeated  filtration  through  the  same  filter.  To  the 
filtrate  add  ammonia-water  until  the  liquid  has  an  alkaline 
reaction.  A  precipitate  will  reappear:  the  phosphate  of 
barium  which  was  dissolved  by  the  hydrochloric  acid  is 
reprecipitated  as  soon  as  the  acid  solvent  is  neutralized  by 
ammonia- water. 

49,  Of  all  the  barium  salts  which  might,  in  an  actual 


§  49.]  THE  BARIUM  TEST.  81 

analysis,  be  precipitated  under  conditions  similar  to  those 
of  the  preceding  experiment,  only  one,  the  sulphate  of 
barium,  is  insoluble  in  dilute  hydrochloric  acid.  A  sepa- 
ration of  sulphur  from  a  hyposulphite  will  not  be  mistaken 
for  a  barium  precipitate  (§  19,  p.  22).  The  fact  that  any 
of  the  original  precipitate  remains  undissolved  by  the 
hydrochloric  acid  demonstrates  the  presence  of  a  sulphate. 
The  portion  of  the  original  precipitate  which  dissolved  in 
the  acid,  and  was  reprecipitated  by  ammonia,  consisted  in 
this  particular  experiment  of  phosphate  of  barium;  but 
in  an  actual  analysis  the  possible  salts  represented  would 
be  so  numerous  as  to  make  the  indication  of  but  little  value ; 
on  the  other  hand,  if  ammonia-water  causes  no  precipita- 
tion, it  must  not  be  inferred  that  the  acid  of  course  dis- 
solved nothing,  for,  with  the  exception  of  the  sulphate,  all 
the  thirteen  above-mentioned  barium  salts  are  more  or  less 
soluble  in  solutions  of  ammonium  salts,  and  if  present  in 
small  quantity  may  not  be  precipitated  on  addition  of  am- 
monia. This  is  especially  true  of  the  borate,  oxalate, 
arseniate,  arsenite,  tartrate  and  fluoride,  and  when  ammo- 
nium -salts  are  known  to  be  present,  there  is  really  but  one 
perfectly  satisfactory  indication  with  chloride  of  barium. 
TJie  presence  of  a  sulphate  is  revealed  by  it  with  certainty,  but 
the  results  of  the  other  tests,  if  negative,  must  be  received 
with  some  distrust. 

It  is  to  be  said,  however,  that  if  the  substance  under 
examination  is  known  to  be  a  simple  salt  and  is  found  to 
be  a  salt  of  ammonium,  the  barium  test  can  hardly  fail  to 
give  a  precipitate  in  alkaline  solution,  if  the  unknown 
compound  is  actually  a  borate,  or  phosphate,  etc.,  of  ammo- 
nium. 

If  the  original  solution  be  acid,  it  is  necessary  to  neutral- 
ize it  with  ammonia-water  before  the  chloride  of  barium  is 
added.  If  a  precipitate  is  produced,  it  is  necessary  to  filter 
and  proceed  with  the  filtrate.     The  precipitate  may  contain 


82  THE  CALCIUM  TEST.  [§§  49,  50. 

phosphates,  oxalates,  etc.,  as  explained  in  §  29,  page  46, 
and  this  must  be  ascertained  by  special  tests,  §§  66,  67,  69, 
etc.  Even  if  ammonia-water  produce  no  precipitate,  the 
testing  is  still  performed  under  the  disadvantage  of  the 
presence  of  ammonium  salts. 

If  the  original  solution  contained  silver  or  lead  salts,  or 
mercurous  salts,  it  would  be  impossible  to  use  chloride  of 
barium  and  hydrochloric  acid  as  reagents;  they  would 
throw  down  the  chlorides  of  those  metals.  Nitrate  of 
barium  (App.,  §  45)  and  dilute  nitric  acid  must  then  be 
used. 

The  acids  added  to  the  precipitate  formed  by  the  barium 
salt  must  be  always  dilute  acids.  Chloride  and  nitrate  of 
barium  are  themselves  insoluble  in  concentrated  hydro- 
chloric and  nitric  acids,  and  if  a  strong  acid  were  used  as 
a  solvent,  the  reagent  salt  might  itself  separate  from  the 
liquid. 

50.  The  Calcium  Test.  —  Chloride  (or  nitrate)  of  calcium 
precipitates  the  same  classes  of  salts  as  chloride  (or  nitrate) 
of  barium,  with*  the  single  exception  of  the  chromates. 
When  sulphates  and  all  ammoniacal  salts  are  absent,  or  pres- 
ent only  in  minute  quantities,  something  may  be  learned 
by  testing  a  neutral  or  slightly  alkaline  solution  supposed 
to  contain  representatives  of  some  of  the  other  classes  of 
salts  enumerated  in  §  47,  with  chloride  or  nitrate  of  calcium. 
The  calcium  salts  liable  to  precipitation  under  these  cir- 
cumstances are  all  soluble  in  acetic  acid,  except  the  oxalate 
and  the  fluoride.  The  precipitate  jjroduced  by  the  calcium 
reagent  is,  therefore,  treated  with  acetic  acid;  if  it  com- 
pletely redissolves,  oxalates  and  fluorides  are  most  probably 
absent.  The  presence  of  notable  quantities  of  ammonium 
salts  renders  this  test  of  uncertain  value,  because  the 
fluoride  and  many  other  salts  of  calcium  are  soluble  in 
solutions  of  ammonium  salts.  Since  sulphate  of  calcium 
is  sparingly  soluble  in  water  and  acetic  acid,  the  presence 


§§  60-53.]  TH:E  StLVEU   TEST.  .  88 

of  a  sulphate,  causing  precipitation  of  sulphate  of  calcium, 
obscures  the  reaction  for  oxalates  and  fluorides.  Nitrate  of 
calcium  must  be  used  instead  of  the  chloride  whenever 
silver  or  lead  salts,  or  mercurous  salts,  are  present  in  the 
solution  under  examination. 

51.  Illustration  of  the  Calcium  Test.  — Prepare  in  a  test- 
tube  an  aqueous  solution  of  phosphate,  oxalate  and  tartrate 
of  sodium  or  potassium.  A  very  small  quantity  of  each 
salt  will  be  enough.  The  solution  will  be  neutral  or  faintly 
alkaline.  Add  to  this  solution  a  solution  of  chloride  of 
calcium  (App.,  §  43)  until  the  precipitation  is  complete.' 
Collect  the  wliite  precipitate  upon  a  filter,  and,  when 
drained,  transfer  it  to  a  test-tube  and  treat  it  with  acetic  acid. 
The  phosphate  and  tartrate  of  calcium  will  redissolve, 
but  the  oxalate  remains  untouched.  To  verify  this  result, 
and  identify  each  one  of  the  classes  of  salts  present  in  the 
original  solution,  special  tests,  to  be  hereafter  described, 
must  be  resorted  to. 

62.  The  Silver  Test. — Nitrate  of  silver  produces  a  pre- 
cipitate in  neutral  or  acid  solutions  with  all  chlorides, 
bromides,  iodides  and  cyanides,  and  in  neutral  solutions 
with  most  of  the  classes  of  salts  enumerated  in  §  47.     In 

.  order  to  obtain  the  most  comprehensive  negative  conclusion 
in  the  case  that  nitrate  of  silver  produces  no  precipitate,  it 
is  necessary  to  operate  upon  a  rieiitral  solution.  If,  on  the 
addition  of  nitrate  of  silver  to  a  neutral  solution,  no  precipi- 
tate appears  after  the  lapse  of  several  minutes,  neither 
chlorides,  bromides,  iodides,  cyanides  nor  sulphides  can  be 
present,  and  the  absence  of  sulphites,  hyposulphites,  car- 
bonates, phosphates,  arseniates,  arsenites,  chromates,  sili- 
cates, oxalates  and  tartrates  may  also  be  inferred  with 
considerable  certainty. 

63.  Illustration  of  the  Silver  Test.  —  Prepare  in  a  test- 
tube  a  weak  solution  of  chloride   of   sodium,    iodide   of 

'potassium,  cyanide  of  potassium  and  phosphate  of  sodium. 


84  THE  SILVER   TEST.  [§§53,64. 

Add  nitrate  of  silver  (App.,  §  40)  to  this  slightly  alkaline 
solution,  until  the  precipitation  is  complete.  The  dense 
precipitate  is  yellowish-white.  Pour  dilute  nitric  acid 
into  the  mixture,  until  the  solution  is  strongly  acid;  shake 
up  the  contents  of  the  tube  thoroughly,  and  after  the  lapse 
of  several  minutes  collect  the  insoluble  precipitate  on  a 
filter,  and  receive  the  filtered  liquid  in  a  test-tube. 

Neutralize  the  filtrate  with  ammon ia- water :  a  yellow 
precipitate  of  phosphate  of  silver  will  reappear. 

Wash  the  precipitate  on  the  filter  thoroughly  to  free  it 
from  the  superfluous  nitrate  of  silver.  Einse  the  washed 
precipitate  into  a  clean  test-tube,  decant  the  water  from 
above  it,  pour  over  it  ammonia-water,  and  gently  heat  the 
mixture.  The  silver  precipitate  will  visibly  diminish  in 
bulk,  but  a  yellowish  portion  remains  undissolved.  Filter 
again,  and  neutralize  the  filtrate  with  nitric  acid;  a  white 
precipitate  will  fall. 

This  experiment  proves  that  a  portion,  but  not  all,  of 
the  mixed  silver  salts  which  are  insoluble  in  nitric  acid, 
are  soluble  in  ammonia-water.  The  chloride,  cyanide  and 
bromide  of  silver  dissolve  in  ammonia-water,  the  latter  with 
difficulty;  the  iodide  remains  undissolved.  Special  tests, 
hereafter  to  be  described,  are  applied  in  order  to  confirm  the 
presence  of  iodine,  and  to  detect  each  and  all  of  the  three 
substances  which  are  liable  to  be  confounded  in  the  white 
precipitate  just  mentioned. 

54.  In  the  application  of  the  silver  test  to  the  examina- 
tion of  a  substance  of  unknown  composition,  it  is,  of  course, 
most  advantageous  to  work  with  a  neutral  solution,  as  in 
such  a  case  the  absence  of  any  precipitate  would  lead  to  the 
inference  that  all  the  salts  mentioned  in  §  52  are  absent :  if 
the  solution  is  neutral,  the  nitrate  of  silver  may  be  added 
directly  to  a  portion  of  it.  In  addition  to  the  classes  of 
salts  mentioned  in  §  52,  if  the  original  solution  contained 
any  considerable  quantity  of  a  borate,  the  borate  of  silver 


§  51.]  THE  SILVER   TEST.  •  85 

would  be  precipitated  under  these  conditions ;  but  a  small 
portion  of  some  borate  might  escape  precipitation.  If  the 
original  solution  be  acid  to  test  paper,  add  nitrate  of  silver 
to  a  portion  of  it  in  a  test-tube,  and  then  pour  in  upon  the 
liquid  some  dilute  ammonia-water,  so  gently  that  the  two 
liquids  do  not  mix  at  once.  At  some  layer  near  the  junc- 
tion of  the  two  dissimilar  liquids,  the  fluid  must  be  neutral. 
If  at  that  layer  no  precipitate  or  cloud  appear,  the  twelve 
kinds  of  salts  above  enumerated  are  absent.  If  the  original 
solution  is  alkaline,  dilute  nitric  acid  is  to  be  added  in 
precisely  the  same  manner  as  the  ammonia-water  in  the 
opposite  case.  The  neutral  layer  between  the  two  liquids 
is  attentively  observed,  and  the  absence  of  any  film  or 
cloud  therein  justifies  the  same  sweeping  conclusion  as  that 
above  given. 

Some  conclusions  may  often  be  drawn  from  the  color  of 
the  precipitate  produced  by  nitrate  of  silver.  Chloride, 
bromide,  cyanide  and  oxalate  of  silver  are  white;  tartrate 
white  becoming  black  on  boiling;  borate  white,  though 
normal  borates  form  in  part  brown  silver  oxide;  iodide, 
phosphate  and  arsenite  of  silver  are  yellow ;  silicate  of  sil- 
ver is  yellow  or  white;  arseniate  of  silver  is  brownish-red; 
chromate  of  silver  is  purplish-red;  sulphide  of  silver  is 
black.  When  the  silver  precipitate  is  white,  black,  or  of 
some  obscure,  indecisive  color,  the  operations  in  the  wet 
way  at  this  stage  should  be  directed  to  proving  or  disprov- 
ing the  presence  of  chlorides,  bromides,  iodides,  cyanides 
and  sulphides.  To  this  end  the  portion  of  the  original 
solution  which  has  been  already  tested  with  nitrate  of  sil- 
ver should  be  made  decidedly  acid  with  dilute  nitric  acid. 
Of  all  the  silver  salts  which  can  be  precipitated  on  the 
addition  of  nitrate  of  silver,  only  the  chloride,  bromide, 
iodide,  cyanide  and  sulphide  can  resist  dilute  nitric  acid. 
If  the  precipitate  once  formed  redissolves  completely  in 
nitric  acid,  no  chloride,  bromide,   iodide,   cyanide  or  sul- 


86  *  THE  SILVER  TEST. 

pliide  was  present  in  the  original  solution.  If,  on  the  con- 
trary, a  residue  remain,  one  or  more  of  these  kinds  of  salts 
must  have  been  represented  in  the  original  solution.  If 
the  residue  be  black  or  blackish,  the  presence  of  a  sulphide 
is  to  be  inferred;  if  it  be  white  or  whitish,  the  absence  of 
sulphides  and  the  presence  of  a  chloride,  bromide  or  cyanide 
is  to  be  inferred;  if  it  be  distinctly  yellowish,  an  iodide  is 
probably  present.  When  the  liquid  under  examination 
contains  a  ferrous  salt,  protochloride  of  tin,  or  any  other 
active  reducing  agent,  metallic  silver  is  liable  to  be  precip- 
itated as  a  dark,  heavy  powder.  The  examination  for  the 
metallic  element  will  generally  have  revealed  the  presence 
of  any  such  agent. 

It  is  to  be  remarked  that  cyanide  of  mercury  does  not 
give  a  precipitate  with  nitrate  of  silver.  When  mercury 
has  been  detected  in  the  substance  under  examination, 
cyanogen  must  be  sought  for  in  other  ways  (§  59)  than  this. 

55.  Nitrates,  Chlorates  and  Acetates.  —  It  is  quite  clear 
that  no  method  of  precipitation  whatever  will  apply  to 
nitrates,  chlorates  and  acetates,  since  no  insoluble  chlorate 
is  known,  and,  with  the  exception  of  some  rather  ill-defined 
basic  compounds,  the  nitrates  and  acetates  are  also  all 
soluble.  Special  tests  must  be  sought  for  these  three  classes 
of  salts. 

It  is  obvious  that  it  is  only  in  the  case  of  the  analysis  of 
substances  soluble  in  water  with  neutral  or  slightly  alkaline 
reaction  that  the  general  tests  are  of  the  greatest  value. 


CHAPTER  X. 

SPECIAL  TESTS  FOR  THE  NON-METALLIC  ELEMENTS. 

56.  We  now  proceed  to  indicate  the  most  available  special 
tests  for  the  non-metallic  elements  and  their  commonest 
compounds.  It  is  noteworthy  that  the  non-metallic  ele- 
ments enter  into  composition  under  various  forms,  which 
produce,  with  one  and  the  same  metallic  element,  various 
salts.  Thus  within  the  narrow  range  of  this  treatise,  sul- 
phur is  to  be  sought  in  sulphides,  sulphates,  sulphites  and 
hyposulphites  (thiosulphates) ;  carbon  in  cyanides,  acetates, 
carbonates,  oxalates  and  tartrates;  and  arsenic  in  arsenites 
and  arseniates.  The  various  classes  of  salts  will  be  taken 
up  successively.  It  should  be  premised  that  these  special 
tests  are  sometimes  applied  to  the  original  solution  before 
the  precipitation  with  chloride  of  barium  and  nitrate  of 
silver,  and  sometimes  during  or  after  these  more  general 
testings.  In  the  first  case,  the  student  is  seeking  guidance 
in  the  application  of  the  more  comprehensive  tests;  in  the 
latter  case,  he  is  trying  to  confirm  results  already  almost 
sure. 

57.  Effervescence.  —  When  a  solution  containing  a  carbo- 
nate, cyanide,  sulphide,  sulphite,  or  hyposulphite,  or  a  mix- 
ture of  representatives  of  some  or  all  of  these  kinds  of 
salts,  is  treated  with  hydrochloric  acid  and  then  warmed,  an 
evolution  of  gas  occurs  with  more  or  less  effervescence.  The 
gases  evolved  are  all  colorless;  but  they  all  have  very 
characteristic  odors  except  carbon  dioxide,  the  gas  which 
escapes  from  a  carbonate.  A  cyanide  gives  off  the  pungent 
odor  of  hydrocyanic  acid.     A  sulphide  yields  sulphuretted 

87 


8d  CARBONATES.  — CYANIDES.  [§§57-59. 

hydrogen  of  familiar  presence.  Sulphurous  acid  gas  (SO^) 
escapes  from  sulphites  and  hyposulphites  (thiosulphates) 
alike;  but  in  the  latter  case  a  deposition  of  sulphur  makes 
the  liquor  turbid.  If  only  one  of  these  gases  were  present, 
the  effervescence  and  the  odor,  or  the  absence  of  odor, 
would  identify  it;  but  when  mixtures  are  to  be  dealt  with, 
further  means  of  identification  are  necessary. 

68.  Carbonates.  —  To  prove  the  presence  of  carbonic  acid 
gas,  when  effervescence  has  occurred,  add  hyrlrnp.hloric  acid, 
little  by  little,  to  the  effervescing  solution,  until  the  acid  is 
decidedly  in  excess ;  meanwhile  keep  the  mouth  of  the  test- 
tube  loosely  closed  with  the  thumb  to  promote  the  accumu- 
lation of  the  gas  evolved.  When  the  tube  is  supposed  to 
be  full,  carefully  decant  the  gas  into  a  second  test-tube 
containing  a  teaspoonful  of  lime-water  (App.,  §  42),  taking 
care  not  to  allow  any  of  the  liquid  to  pass  over  with  the 
gas.  Mix  the  lime-water  and  the  gas  in  the  second  test- 
tube  by  thorough  shaking.  A  white  precipitate  of  carbo- 
nate of  calcium  will  be  produced,  if  the  gas  tested  is,  or 
contains,  carbonic  acid  gas  (COj). 

If  the  effervescence  is  slight,  and  the  quantity  of  gas 
evolved  seems  too  small  to  be  decanted  in  this  way,  dip  the 
end  of  a  dark-colored  glass  rod  into  lime-water,  and  thrust 
the  moistened  end  into  the  test-tube,  bringing  it  close  to  the 
surface  of  the  fluid.  If  the  gas  be  carbonic  acid  gas  the 
lime-water  adhering  to  the  rod  will  become  visibly  turbid. 

The  student  who  desires  to  see  the  working  of  this  test 
before  having  occasion  to  apply  it  in  an  actual  analysis, 
can  operate  upon  a  morsel  of  carbonate  of  sodium  dissolved 
in  a  little  water. 

59.  Cyanides.  —  When  the  smell  of  the  gas  which  escapes 
from  the  solution  under  examination  (§  57),  or  the  qualities 
of  the  precipitate  wjth  nitrate  of  silver  (§  54)  give  occasion 
to  suspect  the  presence  of  a  cyanide,  the  following  confirm- 
atory test  may  be  resorted  to :  —  add  to  the  solution  sup- 


§§  59,  60.]  SULPHIDES.  89 

posed  to  contain  free  hydrocyanic  acid  or  an  alkaline 
cyanide,  a  few  drops  of  a  solution  containing  both  a  ferrous 
and  a  ferric  salt  (a  solution  of  ferrous  sulphate  which  has 
been  exposed  to  the  air,  for  example)  and  a  small  quantity 
of  sodium  hydrate  solution.  A  precipitate  forms,  which,  if 
cyanogen  is  present,  consists  of  a  mixture  of  Prussian  blue 
and  the  hydrates  of  iron.  Warm  the  liquid,  and  add  to  it 
excess  of  hydrochloric  acid ;  the  hydrates  of  iron  dissolve, 
but  the  Prussian  blue  remains  undissolved.  If  the  amount 
of  cyanogen  is  small,  the  hydrates  of  iron,  which  of  course 
always  form,  may  conceal  the  Prussian  blue  until  the  addi- 
tion of  the  acid;  and  in  the  case  of  minute  quantities  the 
liquid  simply  appears  gj-een  after  the  addition  of  hydro- 
chloric acid,  and  it  is  only  after  long  standing  that  a  tri- 
fling blue  precipitate  separates  from  it. 

This  test  may  be  well  illustrated  by  means  of  a  small 
particle  of  cyanide  of  potassium  dissolved  in  a  teaspoonful 
of  water. 

To  detect  cyanogen  in  cyanide  of  mercury,  it  is  necessary 
to  precipitate  the  mercury  as  sulphide,  by  means  of  sulphu- 
retted hydrogen,  and  to  identify  the  free  hydrocyanic  acid 
in  the  filtered  or  decanted  liquid. 

60.  Sulphides. — Many  sulphides  give  off  sulphuretted 
hydrogen  when  heated  with  hydrochloric  acid.  If  the 
quantity  of  gas  is  so  small  that  its  odor  is  imperceptible, 
the  lead  paper  test  (§  33)  should  be  applied. 

When  sulphides  are  dissolved  in  nitric  acid  or  aqua  regia, 
their  sulphur  is  partly  separated  in  a  free  state,  and  partly 
converted  into  sulphuric  acid.  The  free  sulphur  can  be 
identified  by  its  color  and  texture,  and  by  its  behavior 
when  burnt.  The  sulphuric  acid  in  the  liquid  is  detected 
in  the  usual  manner  (§  65). 

If  on  warming  the  substance  to  be  tested  with  hydrochlo- 
ric acid  other  than  a  white  residue  remains,  it  may  contain 
sulphides,  although  no  test  for  sulphuretted  hydrogen  is 


90  SULPBITES.  —  HYPOSULPHITES.       [§§  60^2. 

obtained:  in  this  case,  warm  gently  for  a  few  minutes,  add 
a  granule  of  zinc,  warm,  and  repeat  the  test  with  lead  paper. 
If  no  evidence  of  sulphuretted  hydrogen  is  obtained,  and 
a  colored  residue  still  remains,  remove  the  zinc,  wash  the 
residue  several  times  by  decantation  to  remove  soluble 
sulphates,  treat  with  aqua  regia,  warming  until  no  further 
action  takes  place,  dilute  with  eight  or  ten  parts  of  water, 
filter,  and  to  the  clear  filtrate  add  a  little  chloride  of 
barium  solution  (nitrate  of  barium,  if  lead  or  silver  have 
been  found  in  the  search  for  metallic  elements);  a  white 
precipitate  of  sulphate  of  barium  shows  that  a  sulphide  or 
free  sulphur  was  originally  present. 

61.  Sulphites.  —  All  the  sulphites  evolve  sulphurous  acid 
gas  (SO^),  without  any  deposition  of  sulphur,  when  treated 
with  hydrochloric  acid.  The  very  sharp  odor  of  this  gas 
is  enough  to  identify  it.  Traces  of  sulphurous  acid  gas 
may  be  readily  detected  by  exposing  to  the  gas  in  the  open 
end  of  a  small  tube  a  drop  of  a  mixture  of  ferric  chloride 
solution  and  ferrocyanide  of  potassium,  Prussian  blue  being 
formed  —  resulting  from  the  reduction  of  the  ferric  com- 
pound. 

As  has  been  before  stated,  nitrate  of  silver  produces  in 
solutions  of  sulphites  a  white  precipitate ;  but  this  precipi- 
tate blackens  when  the  liquid  is  boiled,  on  account  of  the 
reduction  of  silver. 

When  the  sulphites  are  heated  with  strong  nitric  acid,  or 
other  powerful  oxidizing  agent,  they  are  converted  into 
sulphates  without  precipitation  of  sulphur.  The  sulphates 
so  produced  may  be  identified  in  the  usual  way  (§  65). 

62.  Hyposulphites  (thiosulphates) . — The  hyposulphites 
disengage  sulphurous  acid  gas  (SO2)  and  deposit  sulphur 
when  warmed  with  hydrochloric  acid.  This  decomposition 
is  not  immediate  if  the  solution  be  dilute.  The  precipitated 
sulphur  is  yellow,  and  not  white,  as  is  usually  the  case  when 
sulphur  separates  in  chemical  reactions. 


§§  62-64.]   CHROMATES.  —  ARSENITES,  AESENIATES.   91 

The  precipitate  produced  in  the  solution  of  a  hyposulphite 
by  nitrate  of  silver  dissolves  again  readily  in  an  excess  of 
the  hyposulphite.  On  standing,  the  precipitate  of  hyposul- 
phite of  silver  turns  black  spontaneously,*being  decomposed 
into  sulphide  of  silver  and  sulphuric  acid.  Heating  pro- 
duces this  eifect  almost  immediately. 

Hyposulphite  of  sodium  is  a  good  salt  from  which  to  get 
the  above  reactions  of  hyposulphites. 

63.  Chromates. — All  chromates  are  yellow  iii  color; 
bichromates  are  orange-red.  Chromium  is  detected  during 
the  examination  for  the  metallic  elements,  and  the  analyst 
generally  obtains  pretty  certain  evidence  concerning  the 
actual  condition  in  which  this  element  enters  into  the  sub- 
stance under  examination,  whether  as  chromate  or  salt  of 
chromium ;  for  the  chromates  are  reduced  by  sulphuretted 
hydrogen  with  change  of  color  and  deposition  of  sulphur, 
as  stated  in  §  23  c.  Unless  reduced  by  sulphuretted  hydro- 
gen, no  precipitate  of  chromium  as  hydrate  will  be  formed 
in  Class  IV. 

To  confirm  the  indications  thus  obtained,  the  following 
tests  are  used:  —  When  acetate  of  lead  (App.,  §  46)  is 
added  to  a  neutral  solution  of  a  chromate,  yellow  chromate 
of  lead  separates,  insoluble  in  acetic  acid,  but  soluble  in 
caustic  soda. 

As  has  been  before  stated,  the  purplish-red  color  of 
chromate  of  silver  (§  54),  and  the  yellow  color  of  chromate 
of  barium  (§  49),  are  valuable  indications  of  the  presence 
of  a  chromate. 

A  solution  of  normal  chromate  of  potassium  is  the  best 
substance  from  which  to  obtain  for  the  first  time  the  reac- 
tions of  the  chromates. 

64.  Arsenites  and  Arseniates. — The  presence  or  absence 
of  arsenic  is  determined  in  the  search  for  the  metallic 
elements  by  the  tests  already  given  in  the  treatment  of 
Class  HI.     These  tests,   however,  do  not  indicate  which 


92  ARSENITES  AND  ARSENIATES.  [§  64. 

class  of  compounds  (arsenic  or  arsenious)  is  present  in  the 
solution  under  examination.  In  whatever  form  present, 
the  arsenic  would  be  precipitated  as  the  trisulphide  (AS2S3), 
and  subsequently^converted  into  an  arseniate  by  fusion  with 
nitrate  of  sodium.  Discriminating  tests  must  therefore  be 
applied  to  the  original  solution. 

The  tests  by  which  an  arseniate  may  be  identified  have 
already  been  given  (§  25,  p.  35).  It  may  be  remarked 
further  that  the  presence  of  this  class  of  arsenic  compounds 
is  often  inferred  by  the  length  of  time  required  to  saturate 
with  sulphuretted  hydrogen  a  solution  containing  arsenic 
acid  or  an  arseniate.  The  arsenic  acid  is  first  reduced  to 
arsenious  acid  and  then  precipitated;  a  separation  of  sul- 
phur accompanies  the  reduction.  Unless  the  solution  is 
hot  the  arsenic  may  not  be  precipitated  as  sulphide^  for 
several  hours. 

A  solution  of  an  arsenite  yields  with  nitrate  of  silver  a 
yellow  precipitate  of  arsenite  of  silver  under  the  same  con- 
ditions in  which  an  arseniate  gives  the  brownish-red  precipi- 
tate. The  silver  test  generally  serves  to  distinguish  between 
arsenites  and  arseniates,  but  circumstances  may  arise  in 
which  it  would  be  inapplicable.  The  following  test  affords 
further  means  of  discrimination :  — 

If  to  a  solution  of  arsenious  acid  or  an  arsenite,  caustic 
soda  be  first  added  in  excess,  and  then  five  or  six  drops  of 
a  dilute  solution  of  sulphate  of  copper,  a  clear  bluish  liquid 
is  obtained,  which,  upon  boiling,  deposits  a  red  precipitate 
of  suboxide  of  copper  (CU2O),  while  soluble  arseniate  of 
sodium  is  simultaneously  produced,  and  remains  in  the 
solution.  This  test  is  good  as  a  means  of  distinguishing 
between  arsenites  and  arseniates  when  no  organic  matters 
are  contained  in  the  solution  under  examination.  The 
qualification  is  necessary,  because  grape-sugar  and  many 
other  organic  substances  exercise  a  like  reducing  action  on 
copper  salts. 


§§64-66.]  SULPHATES. —PHOSPHATES.  93 

In  case  copper  salts  are  present  in  the  solution  to  which 
the  silver  test  for  arseniates  and  arsenites  is  applied,  there 
is  oftentimes  difficulty  in  applying  the  test.  When  copper 
has  been  found  in  the  search  for  metallic  elements,  the  fol- 
lowing method  may  be  employed.  Boil  a  portion  of  the 
original  substance  for  fifteen  or  twenty  minutes  with  three 
or  four  teaspoonfuls  of  a  saturated  solution  of  sodium  car- 
bonate, adding  water  from  time  to  time  as  it  evaporates; 
filter,  and  acidify  the  clear  filtrate  with  nitric  acid,  add 
nitrate  of  silver  solution,  and  then  neutralize  with  ammonia- 
water  :  the  precipitate  of  arseniate,  or  arsenite,  of  silver  will 
appear.  If  the  ammonia-water  is  added  carefully  so  as  not 
to  mix  with  the  acid  solution,  the  precipitate  will  appear 
as  a  thin  film  of  characteristic  color  near  the  junction  of 
the  two  dissimilar  liquids. 

65.  Sulphates.  —  The  barium  test  (§§  47-49)  is  all-suffi- 
cient for  the  detection  of  sulphates.  Sulphate  of  barium 
being  the  only  salt  of  barium  insoluble  in  dilute  acids,  when 
a  white  precipitate  appears  on  the  addition  of  a  solution 
of  chloride  of  barium  to  a  solution  acidified  with  hydro- 
chloric or  nitric  acid,  the  presence  of  sulphuric  acid  or  a 
sulphate  is  shown.  In  case  lead,  silver  or  mercury  in  the 
mercurous  condition  are  present,  nitrate  of  barium  solution 
must  be  used  instead  of  chloride.  It  should  be  remembered 
that  both  chloride  and  nitrate  of  barium  are  themselves 
somewhat  insoluble  in  strongly  acid  solutions;  also  that 
common  nitric  and  hydrochloric  acids  always  contain  traces 
of  sulphuric  acid. 

66.  Phosphates.  —  When  two  or  three  drops  of  a  neutral 
or  nitric  acid  solution  of  a  phosphate  (even  of  iron,  alumi- 
num, barium,  strontium,  calcium  or  magnesium  [compare 
§  29],  are  poured  into  a  test-tube  containing  four  or  five  tea- 
spoonfuls  of  a  solution  of  molybdate  of^ammonium  in  nitric 
acid  (App.,  §  22),  there  is  formed  a  pale  yellow  precip- 
itate which  is  apt  to  gather  upon  the  sides  and  bottom 


94  PHOSPHATES.  [§  66. 

of  the  tube.  The  test  is  best  applied  to  a  nitric  acid  solu- 
tion of  the  substance ;  shaking  vigorously  after  addition  to 
the  molybdate  of  ammonium  solution,  and  if  necessary, 
warming  gently  (not  above  70°  C).  If  the  precipitate  does 
not  appear  in  a  few  minutes,  a  few  drops  more  of  the  solu- 
tion to  be  tested  may  be  added.  Let  the  mixture  stand  for 
at  least  half  an  hour  to  detect  traces  of  phosphoric  acid. 

This  precipitate  is  soluble  in  an  excess  of  phosphoric  and 
other  acids;  and  certain  organic  substances  may  prevent 
its  formation.  A  yellow  coloration  of  the  liquid  merely  is 
not  enough  to  prove  beyond  question  the  presence  of  a 
phosphate ;  a  precipitate  must  be  waited  for.  The  yellow 
precipitate  can  be  easily  recognized,  even  in  dark-colored 
liquids,  when  it  has  settled. 

When  the  previous  steps  of  the  analysis  have  proved  that 
the  phosphates  present  in  the  solution  under  examination 
are  soluble  in  ammoniacal  liquids,  and  that  no  arsenic  acid 
or  arseniates  are  present,  the  following  test  will  identify  a 
phosphate  or  free  phosphoric  acid :  — 

-  Add  to  the  solution  to  be  tested  a  clear  mixture  of  chloride 
of  magnesium,  chloride  of_  ammonium  and  ammonia- water 
(App.,  fif).  When  a  phosphate  or  free  phosphoric  acid 
is  present,  a  white  crystalline  precipitate  of  phosphate  of 
magnesium  and  ammonium  is  formed,  even  in  very  dilute 
solutions.  Stirring  and  shaking  promote  its  separation. 
The  precipitate  dissolves  readily  in  acids. 

When  arsenic  acid  or  arseniates  are  present  in  the  origi- 
nal mixture,  this  test  for  phosphates  can  still  be  applied, 
if  all  the  arsenic  be  previously  removed  by  precipitation  as 
sulphide  (§  25).  The  magnesium  mixture  can  be  used  in 
the  filtrate  from  the  sulphide  of  arsenic,  after  it  has  been 
boiled  to  expel  the  sulphuretted  hydrogen. 

The  magnesium  test  can  only  be  applied  when  the  phos- 
phate present  is  soluble  in  ammoniacal  solutions. 

Phosphate  of  sodium  is  the  best  substance  on  which  to 
try  the  test  for  phosphates. 


§§  67,  68.]  OXALATES.  —  TARTRATES,  95 

67.  Oxalates.  —  The  precipitation  of  white,  finely  divided 
oxalate  of  calcium,  by  all  soluble  calcium  salts  from  solu- 
tions of  oxalates  or  oxalic  acid,  has  been  already  described 
(§  51).  Even  the  solution  of  sulphate  of  calcium  gives  this 
reaction  with  oxalates. 

If  oxalic  acid,  or  an  oxalate  in  the  dry  state,  be  heated 
in  a  test-tube  with  an  excess  of  concentrated  sulphuric  acid, 
a  mixture  of  carbonic  oxide  and  carbonic  acid  is  set  free 
with  effervescence ;  the  carbonic  acid  may  be  identified  by 
the  lime-water  test.  Provided  that  no  carbonate  is  pres- 
ent in  the  substance  to  which  the  test  is  applied,  and  if  the 
quantity  operated  upon  is  considerable,  the  carbonic  oxide 
may  be  inflamed  at  the  mouth  of  the  tube. 

68.  Tartrates.  —  Tartaric  acid  and  the  tartrates,  when 
heated  in  the  dry  state,  char,  and  emit  a  very  character- 
istic odor  which  somewhat  resembles  that  of  burnt  sugar. 
Strong  sulphuric  acid  blackens  tartaric  acid  and  the  tartrates 
on  gently  heating,  while  the  characteristic  odor  of  burnt 
sugar  is  emitted.  This  is  the  only  class  of  salts  amon^ 
all  those  within  the  scope  of  this  treatise,  which  exhibit 
this  carbonization  by  sulphuric  acid. 

To  confirm-  the  presence  of  tartaric  acid,  or  a  tartrate, 
in  any  liquid  supposed  to  contain  it,  a  concentrated  solution 
of  acetate  of  potassium  is  added  to  the  liquid,  and  the  mix- 
ture violently  shaken.  The  precipitate,  when  one  forms,  is 
a  difficultly  soluble  acid  tartrate  of  potassium.  The  addition 
of  an  equal  volume  of  alcohol  increases  the  delicacy  of  the 
reaction.  The  more  concentrated  the  solution  to  be  tested, 
the  better.  To  prepare  the  required  solution  of  acetate  of 
potassium  at  the  moment  of  use,  rub  together  in  a  dish  half  ^ 
a  teaspoonful  of  carbonate  of  potassium  and  as  many  drops 
of  acetic  acid  as  will  dissolve  three  quarters  of  the  carbon- 
ate ;  throw  the  mixture  on  a  small  moistened  filter  and  use 
the  filtrate. 

Tartaric  acid  is  a  good  substance  from  which  to  get  these 
reactions. 


96  BORATES.  —  SILICATES.  —  FLUOBIDES.    [§§  69-71. 

69.  Borates.  —  To  confirm  the  presence  of  a  borate,  strong 
sulphuric  acid  is  mixed  with  the  dry  substance  under  exam- 
ination in  quantity  sufficient  to  make  a  thin  paste,  and  an 
equal  bulk  of  alcohol  is  added  to  the  mixture.  The  alcohol 
is  then  kindled.  Boracic  acid  imparts  to  the  alcohol  flame 
a  yellowish-green  color.  The  test  is  made  more  delicate  by 
stirring  the  mixture,  and  by  repeatedly  extinguishing  and 
rekindling  the  flame.  Copper  salts  impart  a  somewhat 
similar  color  to  the  flame;  but  this  metal,  if  present,  may 
be  got  rid  of  by  sulphuretted  hydrogen  before  testing  for 
boracic  acid. 

The  reactions  of  borates  may  be  obtained  with  a  fragment 
of  borax. 

70.  Silicates.  —  The  silicates  of  sodium  and  potassium 
are  the  only  silicates  which  are  soluble  in  water.  The 
solutions  of  these  alkaline  silicates  are  decomposed  by  all 
acids.  If  hydrochloric  acid  is  added  gradually  to  a  strong 
solution  of  an  alkaline  silicate,  the  greater  part  of  the 
silicic  acid  separates  as  a  gelatinous  hydrate.  As  a  rule, 
the  more  dilute  the  fluid,  the  more  silicic  acid  remains  in 
solution. 

If  the  solution  of  an  alkaline  silicate,  mixed  with  hydro- 
chloric or  nitric  acid  in  excess,  be  evaporated  to  dryness, 
silicic  acid  separates ;  if  the  dry  mass  be  ignited  and  then 
treated  with  dilute  hydrochloric  or  nitric  acid,  the  whole 
of  the  silicic  acid  remains  insoluble  in  the  free  state  as  a 
gritty,  whitish  powder,  while  the  other  substances  dissolve. 

A  solution  of  chloride  of  ammonium  produces  a  gelati- 
npus  precipitate  in  strong  and  moderately  dilute  solutions  of 
the  alkaline  silicates.  This  precipitate  is  hydrated  silicic 
acid  containing  alkali. 

A  solution  of  water-glass  is  the  best  substance  in  which 
to  study  the  reactions  of  the  silicates  of  the  alkali-metals. 

71.  Fluorides.  —  When  a  fluoride,  naturally  combined  or 
artificially  mixed  with  silica,    is  heated  with  strong  sul- 


§  71.]  FLUORIDES.  97 

phuric  acid,  fluoride  of  silicon  is  evolved.  This  reaction 
is  available  as  a  test  for  fluorine.. 

A  mixture  of  the  supposed  fluoride  and  fine  dry  sand  is 
heated  in  a  short,  dry  test-tube  with  concentrated  sulphuric 
acid.  A  drop  of  water,  caught  in  the  loop  of  a  clean  plati- 
num wire,  is  held  in  the  mouth  of  the  test-tube.  This  drop 
of  water  becomes  merely  dim,  quite  opaque,  or  almost  solid 
with  silicic  acid,  according  to  the  quantity  of  fluoride  of 
silicon  evolved  from  the  mixture.  The  gaseous  fluoride  of 
silicon  shows  white  fumes  when  it  comes  in  contact  with 
•^moist  air.  If  a  considerable  quantity  of  fluoride  of  silicon 
be  evolved  from  the  mixture  tested,  it  can  be  decanted  into 
another  test-tube,  and  there  shaken  up  with  water.  If  the 
substance  to  be  tested  for  fluorine  is  known  to  contain 
silica,  it  is,  of  course,  unnecessary  to  add  sand  to  it.  This 
method  applies  to  all  fluorides  decomposable  by  hot  sul- 
phuric acid.  It  is  evident  that  this  test  reversed  can  be 
applied  to  the  detection  of  silica. 

If  a  finely  pulverized  fluoride  is  heated  with  concentrated 
sulphuric  acid  in  a  small  leaden  capsule  or  platinum  cruci- 
ble, hydrofluoric  acid  is  disengaged. 

Coat  with  wax  the  convex  face  of  a  watch-glass  large 
enough  to  cover  the  capsule,  by  heating  the  glass  cautiously, 
and  spreading  a  small  bit  of  wax  evenly  over  it  while  the 
glass  is  hot.  Trace  some  lines  or  letters  through  the  wax 
with  a  pointed  instrument  of  wood  or  horn.  Fill  the  hollow 
of  the  glass  with  cold  water,  and  cover  with  it  the  capsule 
which  contains  the  fluoride  mixture.  Heat  the  capsule  gently 
for  half  an  hour  or  an  hour.  Then  remove  the  watch-glass, 
dry  it,  heat  it  cautiously  to  melt  the  wax,  and  wipe  it  with 
a  bit  of  paper.  The  lines  or  letters  traced  through  the  wax 
will  be  found  etched  into  the  glass.  A  barely  perceptible 
etching  is  made  more  visible  by  breathing  upon  the  glass. 
If  much  silicic  acid  is  present,  this  reaction  fails. 

Fluoride  of  calcium  (fluor-spar)  is  a  good  material  from 
which  to  obtain  these  two  tests  for  fluorine. 


98  CHLORIDES.  —  BROMIDES.  [§§  72,  73. 

72.  Chlorides.  —  The  following  confirmatory  test  may  be 
applied  to  chlorides  in  the  dry  state. 

When  a  chloride,  in  powder,  is  heated  in  a  test-tube  with 
black  oxide  of  manganese  and  strong  sulphuric  ^^^(^^  chlorme 
gas  is  evolved;  this  gas  is  recognized  by  its  odor,  greenish- 
yellow  color  and  reaction  with  iodo-starch  paper.  The  gas 
evolved  by  a  chloride  gives'  no  colored  reaction  with  starch 
alone;  but  when  a  moistened  slip  of  paper,  on  which  a 
mixture  of  starch  paste  and  iodide  of  potassium  (App.,  §  39) 
has  been  spread,  is  held  in  an  atmosphere  or  current  of 
chlorine,  the  paper  is  colored  blue  in  consequence  of  the 
liberation  of  iodine  which  the  chlorine  effects.  The  yellow 
color  of  the  gas  is  IBest  seen  by  looking  lengthwise  through 
the  tube. 

Unless  it  has  been  prepared  artificially  it  is  often  diffi- 
cult to  obtain  black  oxide  of  manganese  which  will  not  of 
itself  give  a  reaction  for  chlorine  when  treated  with  pure 
sulphuric  acid. 

Mercurous  chloride  (calomel)  gives  no  reaction  for  chlo- 
rine when  treated  with  binoxide  of  manganese  and  sulphuric 
acid.  The  chlorine  may  be  detected,  however,  by  treating 
the  salt  in  powder  with  zinc  and  dilute  sulphuric  acid. 
The  mercury  is  reduced  to  the  metallic  state,  and  the  chlo- 
rine goes  into  solution  as  chloride  of  zinc;  in  this  solution 
the  chlorine  may  be  discovered  by  the  ordinary  tests. 

73.  Bromides.  —  The  confirmatory  tests  for  bromides 
depend  upon  the  setting  free  of  bromine  itself. 

Hot  nitric  acid  liberates  the  bromine  from  all  bromides 
except  those  of  silver  and  mercury.  In  solutions,  the  free 
bromine  produces  a  yellow  coloration;  when  set  free  from 
solid  bromides  in  a  long  and  narrow  tube,  the  brownish- 
yellow  vapors  of  bromine  condense  into  a  liquid  upon  the 
cold  walls  of  the  tube. 

When  bromides,  in  powder,  are  heated  in  a  test-tube  with 
black    oxide    of    manganese    and   strong   sulphuric    acid, 


§§  73,  74.]  IODIDES.  99 

brownish-red  vapors  of  bromine  are  evolved.  If  chlorides 
are  also  present,  the  bromine  will  be  mixed  with  chlorine. 

To  identify  bromine  and  distinguish  it  from  chlorine, 
moistened  starch  is  brought  into  contact  with  the  free 
bromine.  A  yellow  or  orange-yellow  coloration  of  the 
starch  marks  the  presence  of  bromine.  To  apply  this  test, 
thrust  a  rod  smeared  with  starch-paste  into  the  tube  which 
contains  the  bromine  vapors ;  or,  when  greater  delicacy  is 
requisite,  perform  the  experiment  which  is  expected  to 
liberate  bromine  in  a  very  small  beaker,  and  cover  this 
beaker  with  a  watch-glass  to  whose  under  side  is  attached 
a  bit  of  paper  moistened  with  starch-paste  and  sprinkled 
with  dry  starch.        , 

Bromide  of  potassium  is  a  good  substance  with  which 
to  study  the  tests  for  bromine. 

74.  Iodides.  —  When  an  iodide,  in  the  solid  form  or  in 
solution,  is  heated  with  strong  nitric  acid,  iodine  is  liber- 
ated and  sublimes  in  violet  vapors. 

Free  iodine  in  vapor  is  recognized  by  the  deep  blue  color 
which  it  imparts  to  starch-paste.  Vapors  may  be  tested 
by  bringing  into  contact  with  them  a  glass  rod  smeared 
with  thin  starch-paste,  or  a  slip  of  white  paper  on  which 
the  paste  has  been  spread. 

The  best  method  of  detecting  iodftie  in  a  solution  is  to 
add  a  few  drops  of  thin,  clear  starch-paste  to  the  liquid, 
and  then  set  free  the  iodine  by  means  of  nitrite  of  potassium 
(App.,  §38),  as  follows:  —  The  cold  fluid  to  be  tested  is 
acidulated  with  dilute  hydrochloric  or  sulphuric  acid,  after 
the  addition  of  the  starch-paste,  and  a  drop  or  two  of  a  con- 
centrated solution  of  nitrite  of  potassium  is  then  added. 
A  dark  blue  color  will  be  instantly  produced.  It  is  essen- 
tial that  the  liquid  should  be  kept  cool,  for  the  blue  colora- 
tion is  destroyed  by  heat. 

Like  chlorine  and  bromine,  iodine  is  liberated  by  heating 
an  iodide  with  black  oxide  of  manganese  and  sulphuric  acid. 


100  IODIDES.  —  BROMIDES.  [§  74. 

The  iodine  so  liberated  is  readily  distinguished  by  the 
above  tests. 

The  student  can  try  all  these  tests  for  iodine  with  a  small 
crystal  of  iodide  of  potassium. 

The  tests  given  in  §§  72-74  are  not  always  satisfactory  or 
conclusive.  The  following  method  is  preferable  and  at 
the  same  time  enables  the  analyst  to  test  for  those  four 
acids  forming  insoluble  salts  of  silver  successively  and  in 
the  presence  of  each  other  in  a  satisfactory  manner. 

In  case  a  nitric  acid  solution  or  aqueous  solution  acidi- 
fied with  nitric  acid  of  any  substance  gives  a  white  or 
whitish  precipitate  on  the  addition  of  nitrate  of  silver  solu- 
tion, chlorides,  bromides,  iodides  or  cyanides  are  presum- 
ably present.  In  ordinary  cases  a  mere  turbidity  indicates 
the  presence  of  a  chloride,  and  other  acids  of  the  group  may 
be  regarded  as  absent.  In  case  a  white  or  whitish  precipi- 
tate insoluble  in  nitric  acid  is  produced  on  the  addition  of 
nitrate  of  silver,  proceed  for  the  detection  of  the  acid  as 
follows :  — 

a.  Boil  about  a. half  a  gram  of  the  original  substance  with 
two  or  three  teaspoonfuls  of  a  saturated  solution  of  carbonate 
of  sodium  for  about  ten  minutes,  replacing  the  water  that 
evaporates ;  dilute  with  an  equal  volume  of  water,  and  filter. 

b.  Iodides.  To  a  portion  of  this  filtrate  add  nitric  acid 
to  strongly  acid  reaction  and  a  few  drops  of  chromate  of 
potassium  solution,  then  add  a  few  drops  of  carbon  bisul- 
phide (App.,  §  64).  Shake  thoroughly;  violet  coloration  of 
the  carbon  bisulphide  shows  the  presence  of  iodine. 

c.  Bromides.  If  no  violet  coloration  of  the  bisulphide  of 
carbon  appears,  add  a  few  drops  of  chlorine  water  (App., 
§  65),  to  the  same  test,  and  shake  thoroughly;  brown  col- 
oration of  the  bisulphide  of  carbon  shows  the  presence  of 
bromine. 

In  case  iodine  was  found  in  the  preceding  test,  filter  out 
the  violet-colored  bisulphide  of  carbon  obtained  through  a 


§  74.]  CYANIDES.  —  CHLORIDES.  101 

wet  filter,  add  half  a  teaspoonful  of  chlorine  water  to  the 
filtrate,  shake  thoroughly,  add  a  few  drops  of  bisulphide  of 
carbon,  and  shake  again ;  bromine,  if  present,  will  color  the 
bisulphide  of  carbon  brown. 

d.  Cyanides.  Acidify  a  portion  of  the  original  filtrate 
with  dilute  sulphuric  acid,  and  test  as  described  in  the  test 
for  cyanides  previously  given  (§  59). 

e.  Chlorides.  If  no  reaction  is  obtained  for  iodine, 
bromine  or  cyanogen  in  the  above  tests,  the  white  precipitate 
produced  by  the  nitrate  of  silver  can  only  be  due  to  the 
presence  of  a  chloride,  and  no  further  test  need  be  made. 

In  case  iodine,  bromine  or  cyanogen  has  been  found, 
acidify  a  portion  of  the  original  filtrate  (a)  with  nitric  acid, 
add  nitrate  of  silver  solution  to  complete  precipitation, 
wash  several  times  by  decantation  and  proceed  as  follows :  — 

/.  Iodine  only  was  found.  Warm  the  precipitate  gently 
for  a  few  minutes  with  ammonia-water,  filter,  and  acidify 
the  filtrate  with  nitric  acid:  chloride  of  silver  is  precipi- 
tated if  present. 

g.  Bromine  was  found,  or  bromine  and  iodine;  cyanogen 
being  absent.  Add  to  the  precipitate  produced  by  nitrate  of 
silver  a  teaspoonful  of  carbonate  of  ammonium  solution, 
pass  carbon  dioxide  through  the  mixture  for  a  short  time, 
warming  gently;  filter,  and  acidify  the  filtrate  with  nitric 
acid :  a  white  precipitate  shows  a  chloride. 

h.  Cyanogen  is  present.  Dry  in  a  small  porcelain  cruci- 
ble or  evaporating-dish,  at  a  gentle  heat,  the  precipitate  pro- 
duced by  addition  of  nitrate  of  silver  to  the  original  filtrate 
acidified  with  nitric  acid,  ignite  to  low  redness  and  allow  to 
cool.  Place  a  bit  of  zinc  in  contact  with  the  residue,  add 
a  little  dilute  sulphuric  acid,  and  allow  action  to  continue 
for  an  hour  or  more ;  dilute  with  an  equal  volume  of  water, 
filter,  and  add  to  the  clear  liquid  nitrate  of  silver  solution. 
The  precipitate  thus  obtained  may  be  tested  as  directed  in 
a,  b,  c  and  d;  but  in  the  absence  of  bromides  or  iodides  a 


102  NITRATES.  [§§  74,  75, 

white  precipitate  at  this  point  is  a  sufficient  test  for  a 
chloride. 

75.  Nitrates.  —  The  preliminary  examination  generally 
gives  warning  of  the  presence  of  a  nitrate :  to  confirm  the 
presence  of  a  nitrate,  one  or  both  of  the  two  following  tests 
may  be  used :  — 

If  the  solution  of  a  nitrate  is  mixed  with  an  equal  volume 
of  strong  sulphuric  acid,  the  mixture  thoroughly  cooled  in 
cold  water,  and  a  concentrated  solution  of  ferrous  sulphate 
then  cautiously  added  to  it  in  such  a  way  that  the  two  fluids 
do  not  mix,  the  stratum  of  ^contact  shows  a  purple  or  red- 
dishcolor,  which  changes  to  a  brown.  If  the  fluids  are  then 
mixed,  a  clear  brownish  liquid  is  obtained.  The  color  fades 
on  heating.  Another  way  of  performing  the  same  test  is 
to  drop  a  crystal  of  ferrous  sulphate  into  the  cold  mixture  of 
nitrate  and  sulphuric  acid.  There  forms  around  the  crystal 
a  dark  halo,  which  disappears  with  a  kind  of  effervescence 
on  the  application  of  heat.  It  is,  of  course,  essential  that 
the  sulphuric  acid  employed  for  this  test  should  be  so  free 
from  nitric  and  hyponitric  acids,  as  not  itself  to  give  this 
reaction  with  ferrous  sulphate.  Chromic  acid  interferes 
with  this. test,  and  if  a  chromate  is  present,  it  must  be 
removed  by  precipitation  with  acetate  of  lead. 

Boil  some  hydrochloric  acid  in  a  test-tube,  add  to  it  one 
or  two  drops  of  a  dilute  solution  of  sulphindigotic  acid 
(App.,  §  58),  and  continue  the  boiling  a  moment.  If  the 
chlorhydric  acid  is  sufficiently  free  from  chlorine,  the 
resulting  liquid  will  be  of  a  faint  blue  color.  If  a  nitrate, 
either  solid  or  in  solution,  be  added  to  this  liquid  and  the 
mixture  be  again  boiled,  the  liquid  will  be  decolorized. 
This  reaction  is  delicate;  but  there  are  some  other  sub- 
stances, especially  free  chlorine,  which  have  a  like  bleach- 
ing effect. 

Nitrate  of  potassium  is  a  suitable  material  on  which  to 
illustrate  the  tests  for  nitrates. 


§§  76, 77.]  CHLORATES.  —  ACETATES.  103 

76.  Chlorates.  —  The  preliminary  examination  gives  warn- 
ing of  the  presence  of  chlorates. 

When  a  few  particles  of  a  chlorate  in  the  solid  form  are 
covered  with  two  or  three  times  as  much  strong  sulphuric 
acid,  and  the  mixture  is  gently  warmed,  the  liquid  becomes 
intensely  yellow,  and  a  greenish-yellow  irritating  gas  of 
peculiar  odor  (chlorine  dioxide,  CIO2)  is  evolved,  which  ex- 
plodes with  violence  at  a  moderate  heat.  After  this  decom- 
position, the  gas  evolved  has  the  characteristic  odor  of 
chlorine.  The  quantity  of  chlorate  operated  upon  sht)uld 
be  very  small. 

The  solution  of  a  chlorate  decolorizes  indigo-solution 
precisely  like  the  solution  of  a  nitrate,  under  like  condi- 
tions (§  75). 

A  chlorate  is  converted  by  ignition  into  a  chloride,  from 
a  solution  of  which  nitrate  of  silver  precipitates  the  chlo- 
rine. 

Chlorate  of  potassium  illustrates  very  well  the  reactions 
of  chlorates. 

T*"  Acetates.  —  When  acetates  are  moderately  heated 
with  strong  sulphuric  acid,  hydrated  acetic  acid  distils  from 
the  mixture,  and  may  be  recognized  by  its  pungent  odor. 

When  an  acetate  is  heated  with  alcohol  and  sulphuric 
acid  in  equal  volumes,  acetic  ether  is  formed.  The  agree- 
able odor  of  this  ether  is  highly  characteristic.  To  be  sure 
of  this  odor,  and  not  mistake  it  for  that  of  other  ethers,  a 
comparison  test  should  always  be  made  with  a  known  ace- 
tate at  the  same  time. 

Hot  concentrated  sulphuric  acid  produces  no  blackening 
with  an  acetate. 

When  a  few  drops  of  a  solution  of  ferric  chloride  (App., 
§  49)  are  added  to  a  solution  of  a  neutral  acetate,  or  to  a 
solution  of  an  acetate  previously  neutralized  with  ammonia, 
the  liquid  acquires  a  dark  red  color,  because  of  the  forma- 
tion of  ferric  acetate.     If  the  liquid  contain  an  excess  of 


104  OXIDES  AND  HYDRATES. 

the  acetate,  a  basic  acetate  of  iron  is  precipitated  in  yellow 
flocks  upon  boiling,  and  the  fluid  finally  becomes  colorless. 

Acetate  of  sodium  may  be  used  to  show  these  reactions. 

78.  Oxides  and  Hydrates.  —  In  case  the  substance  under 
examination  is  an  oxide  or  a  hydrate,  it  may  in  general 
be  recognized  by  the  known  properties  of  the  oxide  or 
hydrate  of  the  metallic  element  which  has  been  found  to 
be  present.  The  hydrates  (except  of  the  alkalies)  give 
off  water  when  heated,  and  many  oxides  and  hydrates  when 
he^ed  with  charcoal  in  a  closed  tube  give  off  carbonic  acid 
or  carbonic  oxide.  Peroxides  may  generally  be  distin- 
guished by  their  giving  off  oxygen  when  heated,  or  by 
causing  an  evolution  of  chlorine  when  treated  with  hydro- 
chloric acid. 

Of  course,  salts  of  most  of  the  oxy-acids,  and,  indeed, 
many  other  substances  besides  oxides  and  hydrates,  give 
carbonic  acid  when  heated  with  carbon.  This  test  miay 
serve  to  identify  a  simple  substance,  but  the  presence  or 
absence  of  an  oxide  in  a  mixture  of  salts  can  often  be  deter- 
mined only  by  quantitative  analysis. 


Part  Second. 


THE    ACTUAL    EXAMINATION    OP    SUBSTANCES    OF    UN- 
KNOWN COMPOSITION. 

79.  The  substance  to  be  examined  may  be  either  solid 
or  liquid.  We  shall  consider  first  the  treatment  of  a  solid; 
afterwards  that  of  a  liquid.  The  solid  may  be  a  metallic 
substance,  that  is,  a  pure  metal  or  an  alloy,  or  it  may  be  a 
salt,  mineral  or  other  non-metallic  body.  The  method  of 
procedure  differs  in  the  two  cases.  We  shall  describe  first 
the  treatment  of  a  salt,  mineral  or  other  non-metallic  sub- 
stance. The  two  following  observations,  however,  apply 
to  all  cases.  The  student  should,  in  the  first  place,  learn  as 
much  as  possible  from  the  external  properties  of  the  sub- 
stance to  be  analyzed,  from  its  color,  consistency  and  odor, 
if  it  is  a  liquid;  from  its  color,  texture,  odor,  lustre,  hard- 
ness, gravity  and  crystalline  or  amorphous  structure,  if  it 
is  a  solid.  By  attentively  observing  the  characteristics  or 
individual  peculiarities  of  every  substance  which  passes 
through  his  hands,  the  student  will  soon  learn  to  recognize 
many  substances  at  sight,  —  by  far  the  quickest  and  easiest 
way  of  identifying  them.  Secondly,  since  the  original  sub- 
stance must  be  several  times  reverted  to  in  order  to  com- 
plete an  analysis,  the  student  should  husband  his  stock  of 
the  substance  to  be  analyzed,  never  employing  the  whole  of 
it  for  any  single  course  of  experiment.  It  is  well  also  to 
reserve  a  portion  for  unforeseen  contingencies. 

105 


CHAPTER  XI. 

TREATMENT   OF    A   SALT,  MINERAL   OR  OTHER  NON- 
METALLIC  SOLID. 

Order  of  Procedure. 

80.  The  general  course  pursued  in  the  analysis  of  a 
non-metallic  solid  substance  consists,  as  a  rule,  in:  —  1st. 
The  preliminary  examination,  to  be  presently  described; 
2d.  The  bringing  the  substance  into  solution;  3d.  The 
examination  of  the  solution  obtained  for  the  metallic  ele- 
ments according  to  the  methods  laid  down  in  Part  I,  Chaps. 
I-VIII;  4th.  The  application  of  such  general  and  special 
tests  for  the  non-metallic  elements  as  may  not  have  been 
rendered  unnecessary  by  facts  observed  during  the  preced- 
ing course  of  the  analysis. 

A.    Preliminary  Examination  in  the  Dry  Way. 

81.  The  preliminary  examination  in  the  dry  way  consists 
essentially  of  two  operations;  the  substance  is  first  sub- 
jected to  the  influence  of  heat  alone  (closed-tube  test,  §  82) ; 
and  afterwards  a  second  portion  of  the  substance,  or,  in 
some  cases,  the  same  portion,  is  exposed  to  the  influence  of 
heat  and  certain  reducing  agents  (reduction  test,  §  83). 

82.  Closed-Tube  Test.  —  Prepare  a  hard  glass  tube  No.  5 
(App.,  §  86),  about  three  inches  long,  and  closed  at  one 
end.  Let  fall  into  this  tube  a  minute  fragment  of  the 
solid,  or  a  little  of  its  powder.  If  the  substance  be  used  in 
powder,  wipe  out  the  tube  with  a  tuft  of  cotton  on  a  wire, 
in  order  that  the  interior  walls  of  the  tube  may  be  clean  to 
receive  a  sublimate.     Heat  the  substance  at  the  end  of  the 

106 


§  82.]  CLOSED-TUBE  TEST.  107 

tube,  at  first  gently  in  the  lamp,  but  finally  intensely  at 
the  highest  temperature  to  be  obtained  with  the  Bunsen 
gas -lamp,  or  in  the  blowpipe  flame.  The  following  are  the 
most  noteworthy  reactions,  with  the  inferences  to  be  drawn 
from  them ;  it  not  unfrequently  happens  that  a  single  sub- 
stance gives  several  of  these  reactions. 

I.  a.  The  substance  blackens,  and  gases  or  vapors  are 
evolved.  These  vapors  often  have  a  disagreeable  smell, 
sometimes  like  that  of  burnt  sugar,  paper  or  feathers. 
Sometimes  they  condense  in  tarry  droplets ;  water  also  con- 
denses on  the  cold  part  of  the  tube.  These  appearances 
indicate  the  presence  of  organic  substances. 

Now  the  presence  of  fixed  organic  matter  interferes  with 
the  detection  of  many  substances,  and  it  must,  as  a  rule, 
be  destroyed  before  the  analysis  can  be  proceeded  with. 
The  method  employed  is  detailed  on  page  115;  no  matter 
whether  the  substance  contains  organic  matter  or  not,  the 
closed-tube  test  is  immediately  succeeded  by  the  reduction 
test.  Simple  blackening  is  not  proof  of  the  presence  of 
organic  bodies.  Some  salts  of  copper  and  cobalt,  for  exam- 
ple, blacken  through  the  formation  of  a  black  oxide. 

When  organic  matter  is  shown  to  be  present,  the  student 
should  look  particularly,  at  the  proper  stage  of  the  analysis, 
for  acetates  (§  77)  and  tartrates  (§  68);  but  he  will  not 
forget  that  there  are  hundreds  of  organic  compounds  which 
are  not  comprehended  in  the  plan  of  this  treatise. 

b.  Certain  other  changes  of  color  are  important.  Zinc 
oxide  and  most  salts  of  zinc  are  yellow  when  hot,  but 
become  white  on  cooling.  Lead  oxide  and  many  lead  salts 
are  yellow  while  hot,  and  remain  yellow  on  cooling.  Bis- 
muth oxide  and  many  bismuth  salts  are  an  orange  to  red- 
brown  while  hot,  pale  yellow  on  cooling.  Ferric  oxide  and 
ferric  salts  are  red  to  black  while  hot,  reddish-brown  when 
cold.  Oxide  of  tin,  yellowish  on  heating,  white  when  cold. 
Red  oxide  of  mercury,  black  when  hot,  red  again  on  cooling. 


108  CLOSED-TUBE  TEST.  [§  82. 

II.  The  substance  is  not  carbonized,  but  vapors  or  gases 
escape  from  it.     The  most  important  are:  — 

a.  Aqueous  vapor,  which  condenses  in  the  upper  part  of 
the  tube.  This  may  indicate  the  presence  of  a  salt  contain- 
ing water  of  crystallization,  or  the  presence  of  a  hydrate,  or 
of  water,  held  mechanically.  Test  the  water  with  litmus 
paper;  if  it  is  alkaline,  ammonia  may  be  suspected;  if  acid, 
some  volatile  acid  (H,,SO„  HCl,  HBr,  HI,  HFl,  HNO3,  etc.). 

b.  Oxygen  recognized  by  its  relighting  a  glowing  match. 
This  gas  indicates  nitrates,  chlorates  and  peroxides,  or  a 
decomposable  oxide  (as  HgO).  If  the  heated  substance 
fuses,  and  a  small  fragment  of  charcoal  thrown  in  is  ener- 
getically consumed,  the  presence  of  a  nitrate  or  chlorate 
may  be  assumed. 

c.  Sulphurous  acid  gas,  recognized  by  its  odor.  It  not 
unfrequently  results  from  the  decomposition  of  sulphites, 
sulphates  and  sulphides. 

d.  Carbonic  acid  gas,  derived  from  decomposable  carbon- 
ates and  some  oxalates,  recognized  by  causing  turbidity  in 
a  drop  of  lime-water  exposed  to  the  escaping  gas. 

e.  Cyanogen,  recognized  by  its  peculiar  odor  and  by  the 
violet  flame  with  which  it  burns  when  there  is  enough  of  it 
to  be  lighted,  derived  from  decomposable  cyanides. 

/.  Sulphuretted  hydrogen,  derived  from  moist  sulphides, 
to  be  known  by  its  odor  and  action  on  lead  paper. 

g.  Acetone,  from  the  decomposition  of  acetates,  recog- 
nized by  its  characteristic  fragrant  odor. 

h.  Ammonia,  resulting  sometimes  from  the  decomposition 
of  ammoniacal  salts,  recognized  by  its  odor.V  '^^<^  - ''  -^^^"^^  /^uj^*- 

III.  Colored  gases  or  vapors  are  set  free. 

a.  Nitrogen  peroxide,  recognized  by  the  brownish-red 
color  of  the  fumes.  It  results  from  the  decomposition  of 
nitrates. 

b.  Bromine,  recognized  by  its  heavy  brownish  fumes  and 
peculiar  odor,  indicating  bromides. 


§  82.]  CLOSED-TUBE  TEST.  109 

c.  Iodine^  violet  fumes  and  peculiar  odor,  indicating 
iodides. 

IV.  A  sublimate  forms  beyond  the  heated  portion  of  the 
tube.     The  whole  of  the  substance  may  volatilize. 

Some  substances,  dissolving  in  the  water  of  crystalliza- 
tion on  heating,  give  deposits  on  the  sides  of  the  tube  which 
may  be  mistaken  for  true  sublimates. 

The  following  are  the  commonest  sublimates :  — 

a.  Ammonium  salts  give  white  sublimates  as  a  rule. 
Unless  the  original  solid  is  obviously  unalterable  by  heat, 
it  should  be  invariably  tested  for  ammonium  by  heating  in  a 
small  test-tube  with  an  equal  bulk  of  slaked  lime  (App., 
§  41)  and  a  few  drops  of  water.  Ammonia,  when  evolved, 
may  be  recognized  by  its  smell  and  by  the  dense  white 
fumes  produced  when  a  rod,  moistened  with  hydrochloric 
acid,  is  held  above  the  mouth  of  the  tube. 

6.  Antimony  trioxide  first  fuses  to  a  yellow  liquid,  and 
then  gives  a  white  sublimate  composed  of  needle-like 
crystals. 

c.    Oxalic  acid  gives  a  white  crystalline  sublimate  with 
dense  fumes  in  the  tube. 
.  d.    Metallic  mercury,  and  some  of  its  compounds. 

The  metal  sublimes  in  minute  globules  if  present  in  the 
first  state,  or  in  the  form  of  easily  reducible  compounds,  as 
mercuric  oxide.  Mercurous  chloride  forms  a  sublimate 
without  first  melting,  which  is  yellow  when  hot;  white 
when  cold. 

Mercuric  chloride  melts  first,  then  sublimes,  forming  a 
white  crystalline  sublimate. 

The  sulphide  of  mercury  gives  a  dull  black  sublimate. 
The  red  iodide  of  mercury  gives  a  yellow  sublimate.  In 
case  indications  of  the  presence  of  mercury  are  obtained, 
they  should  be  confirmed  by  mixing  a  little  of  the  thor- 
oughly dry  substance  with  dry  carbonate  of  sodium,  and 
heating  in  a  closed  tube.     All  compounds  of  mercury  are 


110  CLOSED-TUBE  TEST.  [§82. 

thus  decomposed,  giving  a  sublimate  of  metallic  mercury,  as 
a  gray  mirror  on  the  cold  part  of  the  tube.  With  a  lens 
this  is  seen  to  consist  of  minute  globules ;  and  by  gently 
rubbing  with  a  wire,  globules,  visible  to  the  unaided  eye, 
can  be  obtained. 

e.  Arsenic,  and  some  of  its  compounds.  Metallic  arsenic, 
and  some  arsenical  compounds,  give  a  black  sublimate  of 
metallic  lustre.  The  sulphides  of  arsenic  give  sublimates 
which  are  brownish-red,  sometimes  nearly  black  when  hot, 
but  reddish-yellow  to  red  when  cold ;  these  sublimates  look 
not  unlike  that  of  pure  sulphur.  Arsenious  oxide  gives  a 
white  sublimate,  seen  to  be  crystalline  by  a  lens. 

/.  Sulphur,  free  or  by  the  decomposition  of  some  sul- 
phides, gives  a  sublimate  of  reddish-brown  drops,  which 
becomes  solid  and  yellow,  or  yellowish-brown,  on  cooling. 

Some  other  reactions  of  less  importance  may  occur  in  the 
closed  tube,  and,  in  any  event,  it  is  to  be  observed  that 
the  inferences  to  be  drawn  from  the  appearances  already 
indicated  are  of  very  unequal  value.  Thus  the  detection 
of  organic  matter  is  of  importance,  because,  as  has  been 
stated,  such  matters  must  generally  be  got  rid  of  before  the 
analysis  can  be  proceeded  with.  Again,  the  presence,  or 
entire  absence,  of  ammonium  salts  should  be  put  beyond 
doubt  at  this  first  stage  of  the  examination.  Thirdly,  the 
presence  of  mercury,  or  of  mercurous  salts,  determines  the 
choice  of  the  acid  solvent  in  favor  of  nitric  acid,  in  case 
water  will  not  dissolve  the  substance  under  examination 
(§  87),  and  the  presence  of  mercuric  salts  renders  necessary 
the  substitution  of  sulphide  of  ammonium  for  sulphide  of 
sodium  as  the  solvent  for  the  sulphides  of  Class  III  (§  27). 
Accordingly,  it  is  useful  to  get  information  of  the  pres- 
ence of  mercury  or  its  compounds  at  this  early  stage  of 
the  examination.  As  to  the  other  appearances,  they  give 
information  which  may  be  convenient,  but  is  never  essential 
for  the  safe   conduct  of  the   regular   course  of  analysis. 


§§  82, 83.]  BEBUCfiON   TEST.  Ill 

Practically  the  closed-tube  test  may  generally  be  conducted 
as  follows :  — 

The  substance  is  introduced  into  the  tube  as  stated  above, 
a  strip  of  moistened  litmus  paper  is  folded  loosely  across 
the  mouth  of  the  tube,  and  the  tube  heated  in  the  lamp,  at 
first  very  gently.  The  deportment  of  the  substance  is 
observed  under  the  gentle  heat  at  first  applied  and  also  as 
the  heat  increases,  the  appearance  of  condensed  moisture 
or  of  other  sublimate  is  looked  for,  and  any  action  of  escap- 
ing vapors  on  the  litmus  paper  is  noted.  Meanwhile  the 
tube  is  occasionally  removed  from  the  lamp,  to  see  whether 
any  peculiar  odor  of  escaping  gas  may  be  detected.  Finally, 
any  water  which  may  have  condensed  in  the  tube  is  tested 
with  litmus  paper.  The  student  should  note  any  other 
appearances,  whether  mentioned  above  or  not,  which  mani- 
fest themselves  during  the  examination,  as  they  may  serve 
as  corroborative  tests  when  the  composition  of  the  substance 
has  finally  been  made  out  with  some  certainty. 

83.  Reduction  Test.  —  Mix  a  little  of  the  powder  of  the 
substance  under  examination  (the  bulk  of  a  hemp-seed) 
with  an  equal  quantity  of  carbonate  of  sodium,  and  make 
the  mixture  into  a  pasty  ball  with  a  small  drop  of  water. 
Select  a  piece  of  dry,  well-burned,  soft-wood  charcoal,  and 
cut  out  of  it  a  rectangular  block  about  6  inches  long,  H  in. 
wide,  and  -J-  to  f  in.  thick,  having  its  flat,  smooth  surface 
(6  in.  by  1^  in.)  at  right  angles  to  the  rings  of  growth  in 
the  tree.  It  is  this  surface  which  is  always  to  be  used.  A 
good  piece  of  charcoal  may  be  made  to  serve  for  many  assays 
by  filing  off  the  used  surface  and  exposing  a  new  one,  but 
ordinary  charcoal  allows  portions  of  the  flux  or  even  small 
metallic  globules  to  run  into  its  pores  or  into  cracks  opened 
by  the  heat,  and  can  rarely  be  used  with  advantage  the  sec- 
ond time.  At  a  quarter  to  half  an  inch  from  the  end  of  the 
piece  of  charcoal,  scoop  out  with  a  penknife  a  little  cavity 
of  the  size  of  half  a  pea.     Place  the  prepared  pellet  in  this 


112  REDUCTION   TEST.  [§  83. 

cavity,  and  expose  it  for  several  consecutive  minutes  to  the 
reducing-fiame  of  the  blowpipe  (App.,  §  82). 

Under  these  conditions,  vapors  of  characteristic  odor  or 
appearance  may  be  evolved  ;  some  of  them  will  be  men- 
tioned below.  The  two  objects,  however,  to  which  atten- 
tion is  specially  to  be  directed  are  the  residue  in  the  cavity, 
and  the  incrustation  on  the  charcoal  outside  of  the  cavity. 

The  following  metals  may  be  found  as  fused  metallic 
globules  in  the  cavity;  lead,  silver  and  gold  are  reduced 
with  ease,  even  by  an  inexperienced  operator ;  tin  and  copper 
with  some  difficulty :  — 

a.  Gold  —  a  yellow,  malleable  globule,  produced  without 
incrustation. 

b.  Copper  —  a  red,  malleable  globule,  produced  without 
incrustation. 

c.  Tin  —  a  bright,  white,  malleable  globule.  An  incrus- 
tation is  simultaneously  produced,  which  is  faint  yellow 
when  hot  and  white  when  cold;  it  immediately  surrounds 
the  globule. 

d.  Lead  —  a  very  fusible  and  very  malleable  globule. 
A  yellow  incrustation  is  simultaneously  produced. 

e.  Silver  —  a  brilliant,  white,  malleable  globule,  produced 
without  incrustation. 

/.  Bismuth  —  a  dark  orange-yellow  incrustation,  chang- 
ing to  lemon-yellow  on  cooling.  A  gray,  brittle,  metallic 
globule. 

g.  Antimony  —  a  gray  metallic  globule.  A  white  in- 
crustation. 

h.  Cadmium  —  a  reddish-brown  incrustation;  in  thin  lay- 
ers orange-yellow. 

Common  charcoal  is  itself  very  apt  to  show  a  grayish 
incrustation  of  ash  round  about  the  heated  assay;  this  in- 
crustation remains  unaltered  or  increases,  when  directly 
exposed  to  the  flame.  The  student  should  test  each  piece 
of  charcoal  before  the  blowpipe  flame^  in  order  that  he  may 


§  83.]  nSDXTCTlON  TEST.  113 

not  imagine  a  deposit  of  ash  to  be  an  incrustation  derived 
from  the  substance  under  examination. 

If  a  distinct  globule  has  been  obtained,  it  must  be  picked 
out  with  a  pair  of  jewellers'  tweezers,  and  pounded  on  some 
smooth  and  hard  body  to  test  its  malleability.  If  it  is  mal- 
leable, replace  it  upon  the  charcoal  at  an  unused  spot,  and 
lieat  it  strongly  with  the  oxidizing  flame.  Gold  and  silver 
globules  fuse,  but  maintain  their  brilliancy  and  give  no 
incrustation ;  this  proof  distinguishes  a  genuine  gold  globule 
from  a  yellow  globule  composed  of  an  alloy  of  copper  and 
some  white  metal.  A  yellow  globule  composed  of  oxidiz- 
able  metals  tarnishes  instantly  in  the  oxidizing  flame.  A 
tin  globule  fuses,  but  its  bright  surface  is  instantly  tar- 
nished, and  a  white  incrustation  of  binoxide  of  tin  is  pro- 
duced which  cannot  be  driven  off  by  either  flame.  A  lead 
globule  is  rapidly  converted  into  litharge,  a  yellow  incrus- 
tation being  produced,  which  volatilizes  with  a  bluish 
color  when  touched  with  the  reducing-flame.  A  copper 
globule  is  blackened  by  the  formation  of  oxide  of  copper, 
and  the  blowpipe  flame  is  tinged  with  green. 

Certain  other  phenomena  may  manifest  themselves  dur- 
ing this  experiment  for  the  reduction  of  malleable  metallic 
globules.  Sulphur,  ammonium  salts  in  general,  the  chlo- 
rides, bromides,  iodides  and  sulphides  of  sodium  and  potas- 
sium, the  chlorides  of  lead,  bismuth,  tin  and  copper,  metallic 
mercury,  arsenic,  antimony  and  zinc,  and  many  compounds 
of  these  four  elements,  are  liable  to  pass  off  in  vapors, 
Avhich  are  often  in  part  deposited  upon  the  coal  at  a  greater 
or  less  distance  from  the  hot  assay,  according  to  their  vol- 
atility. With  the  exception  of  sulphur,  these  sublimates 
are  white,  but  when  deposited  in  a  thin  film  upon  the  black 
coal  they  have  a  gray  or  blue  appearance.  During  the  pro- 
duction of  the  arsenic  sublimate  a  peculiar  odor  is  evolved; 
this  sublimate  being  very  volatile  is  only  deposited  at  a  con- 
siderable distance  from  the  assay.     The  incrustation  pro- 


114  HtltotlCTlON   TEST.  [§  83. 

duced  by  zinc  is  distinctly  yellow  while  hot,  but  turns  white 
on  cooling;  it  settles  near  the  assay  and  is  driven  away 
again  with  difficulty.  Nitrates  and  chlorates  generally  give 
warning  of  their  presence  when  heated  on  charcoal  by  caus- 
ing deflagration. 

The  main  object  of  the  experiment  is  the  reduction  of  the 
five  malleable  metals  above  enumerated.  We  may  thus 
obtain  knowledge  of  the  presence  of  gold  (for  a  confirma- 
tory test,  see  §  98,  b).  Tin  generally  gives  warning  of  its 
presence  during  this  experiment ;  and  this  warning  is  of  use, 
because  it  is  inconvenient  to  apply  nitric  acid  as  a  solvent 
to  a  substance  containing  tin,  since  this  reagent  converts  tin 
into  the  very  insoluble  binoxide  of  tin.  The  detection  of 
copper  at  this  stage  is  of  little  advantage.  The  most  im- 
portant fact  deducible  from  the  reduction  test  is  the  pres- 
ence of  either  silver  or  lead.  In  dissolving  an  unknown  sub- 
tance  which  proves  to  be  insoluble  in  water,  it  is  customary 
to  try,  as  the  second  solvent,  hydrochloric  acid.  The  chlo- 
rides of  silver  and  lead  being  insoluble,  or  difficultly  soluble, 
this  acid  should  not  be  used  as  a  solvent  when  either  of 
these  two  metals  is  present.  Nitric  acid  must  be  used  in- 
stead. Moreover,  if  the  substance  has  already  given  evi- 
dence of  the  presence  of  organic  matter  (§  82),  porcelain, 
and  not  platinum,  must  be  used  as  a  support  in  destroying 
the  organic  matter,  as  described  in  the  next  section,  when- 
ever an  easily  reducible  metal  is  present. 

Sometimes,  when  the  substance  under  examination  con- 
tains but  a  small  proportion  of  metal,  some  metal  may  be 
reduced  during  the  blowpipe  experiment  on  charcoal,  but 
the  detached  particles  may  not  run  together  into  a  single 
conspicuous  globule.  Since  a  mistake  as  to  the  presence  of 
a  reducible  metal  may  involve  the  destruction  of  a  plati- 
num crucible,  it  is  best  in  doubtful  cases  to  operate  in  a 
more  delicate  fashion.  To  ascertain,  beyond  question, 
whether  any  reduced  metal   has  been  separated  in  this 


§§88,84.]      DESTRUCTION   OF  ORGANIC  MATTER.       115 

experiment,  moisten  the  cavity  in  the  charcoal  with  water 
after  the  fusion  has  been  finished,  cut  the  charcoal  out  for 
a  little  distance,  both  around  and  below  the  cavity,  and 
transfer  the  contents  of  the  cavity  and  the  scraps  of  charcoal 
to  an  agate  or  porcelain  mortar.  Pulverize  the  whole  mass, 
and  then  carefully  wash  away  the  powdered  charcoal  and  all 
the  lighter  portion  of  the  mixture.  Any  malleable  metal 
that  may  have  been  reduced  remains  in  the  mortar  in  little 
flattened  grains  or  spangles,  in  which  the  peculiar  color  and 
lustre  of  the  metal  or  alloy  are  generally  visible.  Sometimes 
metallic  streaks  are  produced  on  the  mortar  or  pestle  by 
little  particles  of  metal  ground  between  them. 

Iron,  nickel  and  cobalt  when  reduced  on  charcoal  remain 
aftei?  this  washing  as  black  or  dark-gray  powders,  which  are 
attracted  by  a  magnet. 

The  student  must  not  mistake  glistening  particles  of  wet 
charcoal  sticking  to  the  mortar  or  pestle  for  metallic  span- 
gles, and  the  metal  should  be  thoroughly  removed  from  both 
mortar  and  pestle  by  the  use  of  a  few  drops  of  warm  aqua 
regia,  immediately  after  the  experiment  is  finished,  in  order 
to  avoid  errors  on  a  subsequent  occasion. 

84.  Destruction  of  the  Organic  Matter.  —  As  already 
stated  in  §  82,  the  presence  of  fixed  organic  matter  interferes 
with  the  detection  of  many  substances,  and  it  must,  as  a 
rule,  be  destroyed  before  the  analysis  can  proceed.  A  por- 
tion of  the  original  substance,  sufficient  for  the  regular 
course  of  examination  for  the  metallic  elements,  is  ignited 
in  a  porcelain  crucible,  with  free  access  of  air,  or  better,  on 
platinum  foil,  if  the  absence  of  any  easily  reducible  metal 
has  been  proved  by  the  reduction  test,  until  all  the  carbon  is 
burnt  out  of  it.  This  ignition  is  best  performed  on  succes- 
sive small  portions  rather  than  on  a  large  mass  at  once. 

It  is  obvious  that  some  inorganic  volatile  matters  may  be 
lost  during  this  ignition.  Furthermore,  some  substances, 
especially  alumina  and  chromic  and  ferric  oxides,  are  made 


116  SOLUTION.  [§§84, 8& 

very  insoluble  by  ignition.  Exceptionally,  therefore,  the  fol- 
lowing process,  which  is  not  liable  to  these  objections,  is 
employed :  The  substance  in  powder,  paste  or  concentrated 
solution,  is  heated  in  an  evaporating-dish,  with  strong  nitric 
acid,  to  a  temperature  just  below  boiling.  To  this  hot  mix- 
ture chlorate  of  potassium,  in  small  bits,  is  added  gradually 
during  several  minutes,  or  until  the  organic  matter  is  all 
destroyed.  The  solution  is  then  evaporated  to  dryness  on  a 
water-bath;  the  dry  residue  is  moistened  with  strong  hydro- 
chloric acid,  the  mixture  diluted  with  water,  warmed  and 
filtered,  if  there  be  any  residue.  The  filtrate  is  fit  for  the 
regular  course  of  analysis,  except  that  potassium,  having 
been  added,  must  not  be  tested  for  in  this  liquid.  The 
residue,  if  any,  must  be  examined  for  the  insoluble  chlorides 
of  Class  I.  This  process  is  simply  a  combustion  at  a  low 
temperature. 

The  only  classes  of  salts,  coming  within  the  scope  of 
this  manual,  which  in  the  closed-tube  give  evidence  of  the 
presence  of  organic  matter,  are  the  acetates  and  tartrates. 

It  will,  of  course,  be  necessary  to  apply  the  tests  for  acetic 
and  tartaric  acid  to  a  portion  of  the  original  substance  and 
not  to  the  solution  obtained  above.  But  the  student  will 
not  forget  the  statement  already  made  in  §  82,  that  the 
presence  of  organic  matter  does  not  necessarily  imply  the 
presence  of  either  acetates  or  tartrates. 

B.   Dissolving  a  Salt,  Mineral  or  other  Non-Metallic  Solid, 
free  from  Organic  Matter. 

85.  Before  a  solid  substance  can  be  submitted  to  the 
systematic  course  of  analysis,  it  must  be  brought  into  solu- 
tion. There  is  no  universal  solvent.  Different  substances 
require  different  solvents.  The  four  solvents  employed  in 
qualitative  analysis  for  salts,  minerals  and  other  non-metal- 
lic solids,  are  water,  hydrochloric  acid,  nitric  acid  and  aqua 


§§  85,  86.]  SOLUTION.  117 

regia;  and  these  four  liquids  are  to  be  tried  in  the  precise 
order  'in  which  they  here  stand.  Water  is  always  to  be  tried 
first;  to  whatever  resists  water,  strong  hydrochloric  acid  is 
applied ;  if  hydrochloric  acid  fails  to  dissolve  the  solid  com- 
pletely, nitric  acid  is  tried,  and  after  nitric  acid,  aqua  regia, 
as  the  last  resort.  If,  for  reasons  stated  in  §  83,  the  pre- 
liminary examination  has  shown  hydrochloric  acid  to  be 
unsuitable  as  a  solvent,  nitric  acid  is  tried  immediately  after 
water,  and  lastly  aqua  regia  as  before.  A  solid  substance 
should  invariably  be  reduced  to  a  very  fine  powder  before 
being  submitted  to  the  action  of  solvents  (App.,  §  95). 

86.  Dissolving  in  Water.  —  About  half  a  thimbleful  of 
the  powdered  substance  is  boiled  with  ten  times  as  much 
water  in  a  test-tube.  If  an  effervescence  occurs,  as  is 
possible  with  mixtures  containing  an  acid  salt  (yeast-pow- 
ders, for  example),  the  gas  evolved  should  be  carefully 
tested  (§§  57-62).  In  attempting  to  dissolve  a  substance  it 
should  be  remembered  that  several  salts,  whilst  readily  dis- 
solving in  a  small  amount  of  water,  are  decomposed  by  large 
amounts  and  rendered  insoluble.  The  addition  of  a  little  free 
acid  will  usually  prevent  this  decomposition  or  redissolve 
the  basic  salt  formed.  Several  substances  also,  which  are 
soluble  in  cold  or  warm  water,  undergo  decomposition  on 
boiling.  On  this  point  consult  §  88.  If  the  substance  dis- 
solves completely,  the  solution  is  ready  for  analysis.  When 
undissolved  powder  remains  in  the  tube  after  protracted 
boiling,  filter  a  few  drops  of  the  liquid,  and  evaporate  a  drop 
or  two  of  the  filtrate  to  dryness  on  clean  platinum  foil,  at 
as  low  a  heat  as  possible.  If  there  be  no  residue  on  the 
foil,  or  if  the  residue  be  scarcely  appreciable,  the  substance 
is  practically  insoluble  in  water,  and  acids  must  be  tried  as 
solvents.  But  if,  on  the  contrary,  a  tolerable  residue  re- 
mains on  the  foil,  decant  the  liquid  in  the  tube  into  the 
filter,  and  boil  the  powder  again  with  water.  Persevere 
with  this  treatment  until  it  is  evident  that  a  part  of  the 


118  SOLUTION,  [§§86,87. 

powder  is  insoluble  in  water.  The  insoluble  residue  in  the 
test-tube  is  hltered  off;  the  clear  filtrates,  collected  together 
and  concentrated  by  evaporation,  if  of  unreasonable  bulk, 
are  to  be  labelled  "H2O  Sol."  and  reserved  for  the  regular 
course  of  analysis  (§  88).  In  this  case,  and  in  the  still 
more  favorable  case  in  which  all  the  substance  has  dissolved 
in  water,  it  is  a  simple  aqueous  solution  which  is  submitted 
to  analysis. 

87.  Dissolving  in  Acids.  —  The  substance  which  water  has 
failed  to  dissolve,  either  in  whole  or  in  part,  is  next  boiled 
in  a  small  dish  with  three  or  four  times  its  bulk  of  concen- 
trated hydrochloric  acid,  unless  the  tube  test  (§  82  )  or  the 
reduction  test  (§  83)  has  proved  the  presence  of  silver,  lead 
or  mercury;  in  which  case  nitric  acid  is  the  first  acid  to  be 
tried.  If  an  effervescence  occur,  the  escaping  gas  is  to  be 
tested,  as  described  in  §§  57-62.  (See  also  the  last  part 
of  §  78.)  After  boiling  the  powdered  substance  with  the 
strong  acid,  dilute  the  fluid  with  twice  its  bulk  of  water,  and 
repeat  the  boiling  if  any  residue  remain  undissolved.  The 
acid  is  diluted  because,  though  the  substance  to  be  dissolved 
is  best  attacked  in  the  first  instance  by  strong  acid,  the  salts 
formed  by  the  action  of  the  concentrated  acid  are  more 
likely  to  dissolve  readily  in  a  dilute  than  in  a  strongly  acid 
liquor.  Not  a  few  salts,  which  scarcely  dissolve  in  strong 
acids,  are  readily  soluble  in  the  same  acids  when  diluted. 
If  the  whole  of  the  substance  finally  dissolves,  the  solution, 
still  farther  diluted,  is  ready  for  the  transmission  of  sulphu- 
retted hydrogen  (§  20),  for  it  is  of  course  unnecessary  to 
examine  it  for  members  of  Class  I.  If,  on  the  contrary,  an 
undissolved  residue  remain  in  the  tube,  ascertain  if  any- 
thing has  dissolved,  by  carefully  evaporating  two  or  three 
drops  of  the  fluid  to  dryness  on  platinum  foil.  Should  an 
appreciable  residue,  in  excess  of  that  given  by  two  or  three 
drops  of  the  acid  employed,  remain  upon  the  foil,  separate 
the  liquid  in  the  tube  from  the  undissolved  substance  by 

Ik 


§  87.]  SOLUTION.  119 

decantation  or  filtration.  Reserve  the  solution,  labelling 
it  "HClSol." 

Rinse  the  undissolved  powder  with  water,  and  then  boil 
it  in  an  evaporating-dish  with  three  or  four  times  its  bulk 
of  strong  nitric  acid.  If  the  original  substance  contains 
silver,  lead  or  a  mercurous  salt,  hydrochloric  acid  will  not 
have  been  used,  and  it  will  be  the  residue  from  the  aqueous 
solution,  which  is  now  to  be  boiled  with  nitric  acid.  In  this 
case  effervescence  is  to  be  watched  for.  If  the  substance 
dissolves  completely  in  the  strong  acid,  or  dissolves,  with 
the  exception  of  a  light  yellow  mass  of  sulphur,  which  often 
separates  from  a  sulphide,  evaporate  the  liquid  almost  to  dry- 
ness to  drive  olf  the  free  acid,  dilute  the  evaporated  solution 
with  several  times  its  bulk  of  water,  separate  the  sulphur, 
if  necessary,  by  filtration,  and  reserve  the  solution,  label- 
ling it  "HNO3  Sol."  If  the  substance  does  not  completely 
dissolve  in  the  strong  acid,  dilute  the  fluid  with  twice  its 
bulk  of  water,  and  repeat  the  boiling.  If  the  dilute  nitric 
acid  effects  complete  solution,  reserve  the  solution,  labelling 
it  as  before,  "HNO3  Sol."  If  neither  the  strong  nor  the 
diluted  nitric  acid  effects  the  complete  solution  of  the  sub- 
stance, ascertain  if  anything  has  dissolved  in  the  dilute 
acid  by  the  usual  test  on  platinum  foil.  If  an  appreciable 
residue  remain  on  the  foil,  separate  the  undissolved  solid 
in  the  dish  from  the  liquid  by  decantation  or  filtration,  and 
reserve  the  solution. 

Boil  the  powder,  which  has  resisted  both  acids  taken 
singly,  with  aqua  regia.  If  it  dissolves  completely,  evapo- 
rate the  solution  almost  to  dryness,  redissolve  in  water, 
with  the  addition  of  a  little  strong  hydrochloric  acid.  If 
there  be  any  turbidity,  dilute  largely  with  water  and  reserve 
the  solution  for  analysis,  labelling  it,  "Aq.  Reg.  Sol."  It 
is  useless  to  look  for  the  members  of  Class  I  in  such  a 
solution.  If,  on  the  contrary,  it  does  not  completely  dis- 
solve after  protracted  boiling,  test  the  liquor  to  see  if  any- 


120  AN  AQUEOUS  SOLUTION.  [§§  87,  88. 

thing  has  dissolved.  If  an  appreciable  residue  remains  on 
the  foil,  dilute  the  acid  fluid,  filter  it,  reserve  the  solution 
labelled  as  before,  and  wash  the  undissolved  residue  thor- 
oughly with  water,  to  prepare  it  for  further  treatment  (§  88). 

Certain  silicates,  when  boiled  with  concentrated  acids,  are 
decomposed,  and  gelatinous  silicic  acid  is  separated.  This 
happens  but  rarely,  however,  in  the  rapid  processes  of  quali- 
tative analysis;  and  if  it  should  happen,  it  is  not  likely  to 
lead  the  student  into  error.  A  residue  insoluble  in  all  acids 
will  remain;  this  residue  is,  or  contains,  free  silicic  acid. 

It  must  not  be  supposed  that  it  is  common  to  try  all  four 
solvents  on  one  and  the  same  substance.  Water  and  hy- 
drochloric acid  are  the  common  solvents;  nitric  acid  and 
aqua  regia  are,  actually,  but  seldom  resorted  to  as  solvents, 
except  for  metals  (§98).  It  would  require  some  ingenuity 
to  devise  an  artificial  mixture  which  would  put  to  the  test 
all  the  capabilities  of  the  above-described  method  of  bring- 
ing solids  into  solution  in  water  and  acids.  Such  mixtures 
are  not  met  with  in  ordinary  experience.  It  is  the  object 
of  any  method  of  analysis  to  meet  real  problems,  not 
artificial  complications  which  may  be  imagined  but  which 
do  not  occur  in  fact. 


C.    Treatment  of  the  Solutions  Obtained. 

88.  Since  substances  which  prove  to  be  insoluble  in  water 
and  in  acids  must  be  brought  into  solution  by  peculiar 
methods,  we  proceed  to  consider  first  the  treatment  of  the 
solutions  already  obtained. 

I.  An  Aqueous  Solution.  —  If  the  student  is  assured  that 
the  unknown  substance  is  a  simple  salt,  he  may  draw  some 
trustworthy  inferences  from  the  behavior  of  the  substance 
when  solution  in  water  is  attempted.  Of  the  salts  which 
fall  within  the  scope  of  this  manual,  the  following  general 
statements  may  be  made :  — 


§  88.]  AN  AQUEOUS  SOLUTION.  121 

1.  All  salts  of  sodium  and  all  of  potassium  and  ammo-, 
nium,  except  their  double  platinum-chlorides,  are  practically 
soluble  in  water. 

2.  All  normal  nitrates,  chlorates  and  acetates  are  soluble. 
But  some  of  the  basic  salts  of  these  acids  are  insoluble. 
The  nitrates  of  mercury  undergo  decomposition  on  boiling 
with  water,  insoluble  basic  compounds  being  formed.  Ni- 
trate of  bismuth  is  soluble  in  a  small  amount  of  water,  but  is 
decomposed  by  large  amounts,  an  insoluble  basic  nitrate  be- 
ing formed.  The  nitrates  of  tin  are  also  decomposed  by  water. 

3.  All  normal  cJilorides  except  silver,  mercurous  and 
cuprous  chlorides,  and  the  double  platinum-chlorides  of 
potassium  and  ammonium  are  soluble.  Chloride  of  lead 
dissolves  but  sparingly  in  cold  water.  Stannous  chloride 
is  soluble  in  a  small  amount  of  water,  but  decomposes  in  the 
presence  of  large  amounts ;  the  same  is  true  of  the  chlorides 
of  bismuth  and  antimony,  insoluble  basic  chlorides  being 
formed  if  much  water  is  present. 

4.  All  normal  bromides  are  soluble  except  silver,  mercu- 
rous and  cuprous  bromide.  Bromide  of  lead  and  mercurous 
bromide  are  with  difficulty  soluble.  Bismuth  and  antimony 
bromide  are  decomposed  by  water. 

5.  Iodides  behave  in  a  similar  manner  to  bromides. 
Iodide  of  lead  is  even  less  soluble  than  bromide. 

6.  Sulphates.  The  sulphates  of  barium,  strontium  and 
lead  and  several  basic  sulphates  are  insoluble  in  water. 
Sulphates  of  antimony  and  bismuth  are  decomposed,  form- 
ing insoluble  basic  compounds.  Mercurous,  silver  and  cal- 
cium sulphate  are  soluble  with  great  difficulty. 

7.  All  the  sulphides  of  sodium,  potassium  and  ammo- 
nium are  soluble.  The  sulphides  of  calcium,  magnesium 
and  barium  prepared  in  the  dry  way  are  soluble  with  great 
difficulty.  The  polysulphides  and  sulphydrates  of  these 
elements  are  quite  readily  soluble. 

8.  None  of  the  normal  carbonates,  arseniates,  arsenites. 


122  AN  AQUEOUS  SOLUTION.  [§  88. 

phosphates  or  borates  besides  those  of  the  alkali  metals  are 
readily  soluble  in  water.  Several  acid  phosphates  and  acid 
carbonates  are  readily  soluble. 

9.  A  few  cyanides,  oxalates,  tartrates,  chromates  and 
sulphites,  besides  those  of  the  alkali  metals  already  men- 
tioned, are  soluble. 

It  is  obvious  that  any  element  of  the  thirty-six  considered 
in  this  treatise  may  be  present  in  an  aqueous  solution ;  but 
it  is  also  evident  from  the  above  list  that  a  great  number 
of  salts  are  absolutely  excluded  because  of  their  insolubility 
in  water. 

If,  on  the  contrary,  there  is  no  certainty  that  the  substance 
under  examination  is  not  a  complex  artificial  mixture,  few 
conclusions  can  be  safely  drawn  from  the  fact  that  a  part  of 
it  or  the  whole  of  it  dissolves  in  water. 

Test  the  solution  with  litmus  paper.  The  solution  is 
either  neutral,  acid  or  alkaline. 

a.  The  solution  is  neutral.  The  normal  salts  of  most  of 
the  metals  have  an  acid  reaction.  Sodium,  potassium,  ba- 
rium, strontium,  calcium,  magnesium,  manganese  and  sil- 
ver are  the  only  metallic  elements  which  form  salts  whose 
solutions  are  neutral.  Add  to  two  or  three  drops  of  the 
solution  a  drop  or  two  of  carbonate  of  sodium.  If  a  pre- 
cipitate forms,  any  of  the  above-mentioned  elements  may  be 
present,  and  are  to  be  tested  for  in  regular  course  according 
to  the  methods  of  Part  I;  if  no  precipitation  ensues,  only 
sodium  and  potassium  or  ammonium  can  be  present,  and 
they  may  be  tested  for  directly,  as  described  in  Chap.  VIII. 

b.  The  solution  is  acid.  The  acidity  may  be  caused  by 
a  normal  salt  having  an  acid  reaction,  or  by  an  acid  salt. 

Neither  carbonates  nor  sulphides  can  be  present  in  an 
aqueous  solution  with  an  acid  reaction.  The  solution  is  to 
be  tested  for  the  metallic  elements  in  the  usual  manner. 

c.  The  solution  is  alkaline.  The  alkalinity  may  be  due 
to  the  hydrates,  sulphides,  cyanides  or  carbonates  of  the 


§  88.]  AN  AQUEOUS  SOLUTION.  123 

metals  belonging  to  Classes  VI  and  VII ;  to  the  presence  of 
a  borate,  silicate,  phosphate,  arseniate,  arsenite  or  alumi- 
nate  of  sodium  or  potassium ;  to  free  ammonia  or  to  carbo- 
nate of  ammonium.  If  the  alkalinity  proceed  from  an 
alkaline  sulphide,  the  metals  whose  sulphides  are  insoluble 
in  water  and  in  alkaline  sulphides  must  be  absent.  If  it 
is  due  to  the  presence  of  the  hydrates  or  carbonates  of  the 
metals  of  Classes  VI  and  VII,  a  very  large  number  of  sub- 
stances are  excluded.  If  it  proceed  from  ammonia  or  car- 
bonate of  ammonium,  all  substances  precipitable  by  these 
reagents  are  absent. 

An  alkaline  solution  may  obviously  contain  some  sub- 
stance, soluble  in  an  alkaline  solvent  like  sodium  hydrate 
or  sulphide  of  ammonium,  but  liable  to  immediate  precipi- 
tation when  this  solvent  is  destroyed  by  the  addition  of 
hydrochloric  acid  at  the  first  step  of  the  analysis.  Thus 
any  sulphide  of  Class  III  dissolved  in  caustic  soda  or  in  an 
alkaline  sulphide,  or  compounds  of  alkaline  hydrates  with 
the  hydrates  of  aluminum,  zinc  or  chromium,  would  be  pre- 
cipitated when  the  alkaline  solvd!it  was  neutralized. 

Again,  the  alkaline  solution  of  a  silicate  of  sodium  or 
potassium,  when  neutralized  with  acid,  yields  a  very  gelat- 
inous whitish  preci]3itate  of  hydrated  silicic  acid.  From  a 
very  concentrated  solution  of  a  borate,  boracic  acid  separates 
in  colorless,  shining,  flat  crystals,  when  the  solution  is 
acidified  with  hydrochloric  acid ;  but  the  boracic  acid  thus 
separated  dissolves  when  the  solution  is  diluted.  Again 
(although,  of  course,  this  could  not  happen  in  the  case  of 
an  alkaline  solution  actually  made  by  dissolving  a  solid  sub- 
stance in  water),  chloride  of  silver  dissolved  in  ammonia- 
water  would  be  thrown  down  by  any  acid  added  in  excess 
to  the  solution.  (§  17,  page  21.)  An  alkaline  solution 
containing  a  poly  sulphide  or  a  thiosulphate  would  give  a 
precipitate  of  sulphur  on  acidifying  it. 

In  view  of  these  possibilities,  an  alkaline  aqueous  solution 


124  AN  AQUEOUS  SOLUTION.  [§  88. 

should  be  carefully  neutralized  with  nitric  acid,  as  a  pre- 
liminary measure,  before  hydrochloric  acid  is  added  to  it. 
Effervescence  should  be  watched  for,  and,  if  it  occurs, 
studied  as  directed  in  §§  57-62.     Several  different  cases  of 
precipitation  may  be  distinguished,  requiring  somewhat  dif- 
ferent treatment.  - 
^*— ^  a.    If  the  characteristic  gelatinous  precipitate  of  silicic 
I      acid  appears,  the  acidulated  solution  must  be  evaporated  to 
I     dryness  and  ignited.     The   silicic   acid   is   thus   rendered 
I     insoluble.    The  ignited  residue  is  digested  with  dilute  nitric 
I    acid  and  filtered.     The  filtrate  is  ready  for  the  usual  course 
1    of  analysis.     The  insoluble  residue  is  silicic  acid. 

b.  If  the  glistening  colorless  plates  of  boracic  acid  ap- 
pear, dilution  with  warm  water  will  cause  them  to  redissolve. 

c.  If  a  precipitate  appear  on  neutralization,  whose  color 
or  texture  proves  that  it  is  neither  silicic  nor  boracic  acid, 
but  some  substance  insoluble  in  water  and  dilute  acids, 
thrown  down  in  consequence  of  the  destruction  of  its  alka- 
line solvent,  the  liquid  is  made  slightly  acid  and  then  fil- 
tered.   The  filtrate  is  ready  for  the  usual  course  of  analysis. 

The  precipitate,  rinsed  with  a  little  water,  is  reserved 
for  further  treatment ;  it  is  not  properly  a  substance  soluble 
in  water,  and  it  must  be  brought  into  solution  by  other 
methods,  hereafter  to  be  described.  Sometimes  a  precipi- 
tate forms  on  exact  neutralization  of  an  alkaline  fluid, 
which  redissolves  when  the  acid  is  added  in  excess. 

II.  An  Acid  Solution.  —  Of  the  three  kinds  of  acid  solu- 
tions described  in  §  87,  any  one,  any  two,  or  all  three,  may 
be  obtained  from  a  single  mixture  of  different  solids. 
There  is  an  advantage  in  knowing  that  a  part  of  a  complex 
mixture  is  soluble  in  water,  a  part  in  hydrochloric  acid,  a 
part  in  nitric  acid  and  a  part  only  in  aqua  regia;  because 
this  knowledge  may  enable  the  student,  when  he  has  found 
out  all  the  elements  of  the  mixture,  to  make  a  more 
probable  guess  at  the  manner  of  their  combination  in  the 


§  88,  89.]  AN  ACID   SOLUTION.  125 

original  mixture,  than  he  would  otherwise  be  able  to.  But 
it  is  usually  unnecessary  to  keep  the  three  kinds  of  acid 
solution  apart,  when  all  three  have  been  obtained,  and  to 
analyze  them  separately.  On  the  contrary,  all  three  should 
be  mixed  together,  and  analyzed  in  one  course  of  testing. 
It  must  only  be  borne  in  mind  that  when  lead,  silver,  or 
mercurous  salts  are  present,  the  nitric  acid  solution  of  the 
residue  from  the  aqueous  solution  will  give  a  precipitate 
of  the  insoluble  chlorides  of  Class  I,  on  being  mixed  with  a 
hydrochloric  acid  or  aqua  regia  solution,  and  also  that  in 
some  cases  the  mixing  of  the  several  solutions  may  cause  the 
formation  of  an  insoluble  precipitate  by  reactions  between 
bodies  in  solution.  It  is  therefore  advisable  to  mix  a  small 
portion  of  the  various  solutions  and  see  whether  any  tur- 
bidity or  precipitate  is  formed.  If  none  appears,  the  solu- 
tions may  be  safely  mixed  and  the  analysis  proceeded  with. 
If^  however,  an  insoluble  precipitate  does  appear,  the  several 
solutions  must  be  analyzed  separately. 

The  student  must  be  careful  to  use  no  more  acid  than  is 
absolutely  essential.  Nitric  acid,  particularly,  is  very  ob- 
jectionable ;  because  when  free  it  reacts  upon  sulphuretted 
hydrogen  with  mutual  decomposition,  sulphur  being  set 
free.  It  has,  therefore,  been  already  prescribed  to  remove 
the  free  acid  by  evaporation.  Sometimes  a  strongly  acid 
solution  becomes  turbid  when  merely  diluted  with  water. 
This  phenomenon  points  to  the  presence  of  bismuth  or 
antimony.  The  turbidity  will  disappear  again  on  the  addi- 
tion of  hydrochloric  acid. 

The  mixed  acid  solutions,  after  the  filtration  from  any 
precipitated  chlorides  of  Class  I,  as  first  mentioned,  are 
submitted  to  the  regular  course  of  analysis  for  the  metallic 
elements. 

89.  Examination  of  the  Solutions  for  the  Non-metallic 
Elements.  —  As  has  been  already  stated  in  §  43,  the  exami- 
nation for  the  non-metallic  elements  generally  follows  that 


126         TESTS  FOR  NON-METALLIC  ELEMENTS.       [§  89. 

for  tlie  metallic  elements.  The  method  of  procedure  is 
usually  as  follows :  —  If  the  substance  is  soluble  in  water 
and  there  is  reason  to  believe  that  it  is  not  a  complex  arti- 
ficial mixture,  but  a  simple  substance,  the  determination 
of  the  metallic  element  generally  proclaims  the  absence  of 
certain  classes  of  salts,  so  that  it  is  very  seldom  necessary 
to  apply  more  than  the  barium  and  the  silver  tests  and  a 
few  special  tests.  This  will  best  be  illustrated  by  taking 
two  examples. 

Suppose  a  homogeneous  solid,  which  dissolves  readily  in 
water,  and  which  proves  to  contain  strontium.  Of  the 
classes  of  salts  coming  within  the  range  of  this  manual 
(see  p.  78),  only  the  sulphide,  chloride,  bromide,  iodide, 
cyanide,  nitrate,  chlorate  and  acetate  of  strontium  are  sol- 
uble in  water;  the  presence  or  absence  of  a  sulphide  (and 
probably  of  a  cyanide)  will  have  been  shown  when  hydro- 
chloric acid  was  added  to  precipitate  the  members  of 
Class  I;  the  silver  test  will  show  either  the  presence  or 
absence  of  the  chloride,  bromide,  iodide  and  cyanide,  and 
these  various  classes  of  salts,  if  any  are  present,  must  be 
distinguished  by  special  tests;  special  tests  must  also  be 
applied  for  nitrates  and  chlorates,  and  also  for  acetates  if  the 
substance  blackened  in  the  closed  tube.  In  this  case,  then, 
the  silver  test  is  the  only  general  test  necessary,  and  the  num- 
ber of  special  tests  should  hardly  be  more  than  four  or  five. 

Again,  suppose  the  substance  soluble  in  water  proves  to 
contain  a  mercurous  salt,  the  only  classes  of  salts  to  be 
sought  for  would  be  the  sulphate  (to  be  decided  by  the 
barium  test),  the  cyanide,  chlorate,  nitrate  and  acetate  (to 
be  determined  by  special  test). 

If  the  only  metallic  element  found  in  an  aqueous  solution 
were  sodium  or  potassium  (or  the  radical  ammonium),  it 
would  be  necessary  to  look  for  all  the  classes  of  salts  enu- 
merated on  page  78.  In  this  case  the  barium  test  would  be 
applied  first,  then  the  silver  test,  then  such  special  tests  as 


§  89.]       TESTS  FOE  NON-METALLIC  ELEMENTS.         127 

had  not  been  rendered  unnecessary  by  negative  evidence 
obtained  from  the  general  tests.  The  calcium  test  would 
also  be  applied  if  the  barium  test  had  made  the  presence  of 
an  oxalate,  tartrate  or  fluoride  not  impossible. 

In  the  case  of  an  acid  solution  the  conclusions  to  be 
drawn  from  the  presence  of  certain  metallic  elements  are 
not  so  general,  still  in  the  case  of  simple  substances  the  ab- 
sence of  certain  classes  of  salts  will  generally  be  made  sure. 
For  example,  a  substance  under  examination,  presumptively 
a  simple  salt,  proves  to  be  insoluble  in  water,  soluble  in 
hydrochloric  acid  and  to  contain  nickel.  The  sulphate,  chlo- 
ride, bromide,  iodide,  chlorate,  acetate  and  nitrate  of  nickel 
are  soluble  in  water,  and  for  this  reason  are  excluded  from 
consideration;  the  sulphite,  hyposulphite,  sulphide,  arseni- 
ate,  arsenite  and  carbonate  would  have  revealed  themselves 
in  the  course  of  the  examination  for  the  metallic  elements, 
and  the  only  salts  to  be  specially  tested  for  at  this  point 
are  the  phosphate,  oxalate,  tartrate  and  silicate.  If  the 
general  and  special  tests  fail  to  indicate  the  presence  of 
any  of  the  classes  of  salts  mentioned  on  page  78,  the  sub- 
stance may  be  an  oxide  or  hydrate.  The  hydrates  give  off 
water  when  heated  in  a  closed  tube ;  peroxides  sometimes 
give  off  oxygen  under  the  same  conditions,  and  most  ox- 
ides, when  mixed  with  an  excess  of  carbon  and  heated,  give 
off  carbonic  oxide,  or  carbonic  acid  gas ;  these  gases  may  be 
recognized  as  stated  on  page  95  under  oxalates. 

It  is  evident  from  what  has  just  been  said,  that  a  knowl- 
edge of  the  solubility  of  chemical  compounds  is  of  great 
value  in  determining  the  presence  or  absence  of  various 
classes  of  salts.  The  student  of  qualitative  analysis  should 
always  have  at  hand  a  copy  of  some  work  on  general  chem- 
istry to  which  he  can  turn ;  but  for  convenience  of  reference, 
a  table  will  be  found  on  pages  128,  129,  in  which  are  stated 
in  a  general  way  the  solubilities  of  the  more  commonly 
occurring  salts. 


128        SOLUBILITIES  OF  CHEMICAL  COMPOUNDS.      [§  89. 

Table  of 


Al  [NH4] 

|Sb 

As 

Ba 

Bi 

Cd 

Ca 

Cr"i 

Co 

Cu 

Au 

Pe» 

Fe^ 

Acetate 

W, 

W 

u 

U 

W 

W 

W 

W 

Wi 

W 

Wi 

U 

W 

Wi 

Arseniate 

A 

W 

u 

u 

A 

(A) 

U 

A 

A 

A 

A 

u 

A 

A 

Arsenite 

U 

w 

u 

u 

(W) 

U 

u 

A 

U 

A 

A. 

u 

A 

A 

Borate 

u 

w 

u 

u 

(W) 
A 

A 

(W) 

(W) 

A 

(W) 
A 

(W) 
A 

U 

A 

A 

Bromide 

w 

w 

(We)  (W) 

W 

(We) 

W 

W 

W 

W 

W4 

W 

W 

W 

Al 

A 

Al 

Carbonate 

u 

w 

u 

u 

A 

A 

A 

A 

A 

A 

A 

u 

A 

A 

Chlorate 

w 

w 

u 

u 

W 

u 

W 

W 

u 

W 

W 

u 

W 

W 

Chloride 

w 

w 

"■1: 

A 

W 

We 

Al 

W 

W 

w 

W 

w, 

w 

W 

W 

Chromate 

A 

w 

A 

U 

A 

A 

(W) 
A 

(W) 

A 

A 

(W) 

u 

U 

A 

Cyanide 

u 

w 

u 

U 

(W) 

U 

(W) 

w 

A 

A 

A 

W5 

(A) 

W 

Fluoride 

1 

w 

w 

W 

(W) 

W 

(W) 

I 

W 

(W) 

(W) 

u' 

(W) 

(W) 

Hydrate 

A 

w 

A-I 

A 

(W) 

A 

A 

(W) 

A 

A 

A 

A 

A 

A 

''lu:'- 

U 

w 

u 

u 

(W) 
A 

U 

W 

w 

U 

W 

U 

U 

W 

U 

Iodide 

w 

w 

(We)  (W) 

w 

A 

W 

w 

W 

W 

U4 

A 

W 

w 

Nitrate 

w 

w 

u 

U 

w 

We 
A, 

W 

w 

w 

W 

w 

W 

W 

w 

Oxalate 

A 

w 

u 

u 

A 

-"1 
A 

A 

A 

w 

A 

A 

u 

A 

A 

Oxide 

A 

w 

A 

w 

W 

A 

A 

(W) 

A-I 

A 

A 

A 

A 

A 

Phosphate 

!   A 

w 

(W) 
A 

u 

Aj 

A 

A 

A2 

A 

A 

A 

u 

A 

A 

Silicate 

A-I 

u 

U 

u 

A-I 

U 

U 

A-I 

U 

U 

A-I 

U 

(A)-I  (A).I 

Sulphate 

W 

w 

A 

u 

I 

A 

W 

(W) 
A 

w 

w 

W 

u 

W 

Wi 

Sulphide 

u 

w 

A 

A 

W 

A 

A 

(W)8 

u 

A 

A 

A 

A 

u 

Sulphite 

W 

w 

U 

U 

A 

A 

A 

(W) 
A 

A 

A 

A 

U 

(W) 

A 

Tartrate 

W 

w 

W 

u 

(W) 
A 

A 

(W) 

(W) 

W 

W 

(W) 

U 

(W) 

W 

Al  [NH4; 

|Sb 

As 

Ba 

Bi 

Cd 

Ca 

Cr»i 

Co 

Cu 

Au 

Fe« 

Fe"» 

' 

In  this  table  W  signifies  that  the  substance  is  readiljr  soluble  in  water, 
(W)  that  the  substance  is  soluble  with  difficulty  in  water,  ^  .  ^  that  the 
substance  is  sparingly  soluble  in  water,  readily  soluble  in  acids  ;  A  and 
(A)  that  the  substance  is  readily  or  with  difficulty  dissolved  by  acids ;  I 
that  the  substance  is  insoluble  in  water  or  acids  ;  U  signifies  that  the 
compound  is  either  unknown  or  so  uncommon  as  rarely  to  be  mej^with. 


§89.]       SOLUBILITIES   OF  CHEMICAL   COMPOUNDS.       129 
Solubilities. 


Pb  Mg 

Mn 

Hgr> 

Hg" 

Ni 

Pt 

K 

Agr 

Na 

Sr 

Sii« 

Sn'» 

Zn 

W 
A 
A 
A 

w 

A 
A 
A 

W 
A 
A 
A 

(W) 
A 
A 
U 

W 
A 
A 
U 

W 
A 
A 
A 

u 
u 
u 
u 

W 
W 
W 

w 

(W) 

A 

A 

(W) 
A 

W 
W 

w 

w 

A 

A 

(W) 

w 

A 
A 
A 

W 

A 
A 

U 

W 
A 

U 
A 

Acetate 

Arseuiate 

Arsenite 

Borate 

(W) 

W 

W 

A 

(W) 

W 

w 

w 

(A) 

w 

w 

W 

w 

W 

Bromide 

A 
W 

(W) 

A 
W 
W 

A 

U 

w 

A 
W 

(A) 

A 
W 
W 

A 
W 
W 

A 

u 
w 

w 
w 

A 
W 

(A)-I 

w 
w 

A 
W 
W 

A 
W 
W 

A 
W 
W 

A 
\V 
W 

Carbonate 

Chlorate 

Chloride 

A 

W 

u 

A 

(W) 

A 

u 

w^ 

A 

w 

(W) 

A 

u 

W, 

Chromate 

A 
A 

(W) 

W 

(AJ 

A 

A 
A 

A 

U 
A 

A 

w 
w 

A 

(A) 
(W) 

A 

A 

(A) 

w 

A 

w 
w 

w 

A 
W 

A 

w 
w 

w 

u 

(W) 
(W) 

u 
w 

A 

u 
w 

A 

A    Cyanide 
(W)  Fluoride 
A 
A    Hydrate 

(W) 
A 

(W) 

W 
W 

W 
W 

U 
A 

U 
A 

W 
W 

U 
I 

w 
w 

(W) 
A 
A 

w 
w 

w 
w 

W 

(W) 

u 

(W) 

U 
W 

Iodide 

w 

W 

W 

W, 

w, 

W 

W 

w 

W 

w 

w 

A 

A 

W 

Nitrate 

A 

(W)  (W) 

A 

A 

A 

W 

w. 

(W) 

w 

A 

A 

W 

A 

Oxalate 

A 
A 

A 
A 

A 
A 

A 
A 

A 
A 

A 
A 

A 
U 

w 
w 

A 
A 

w 
w 

(W) 
A, 

A 

A 

I 
A 

A 
A 

Oxide 
Phosphate 

U 

I 

I 
W 

(A)-] 
W 

:   u 

(W) 

U 
W 

U 
W 

U 
W 

w 

U 

(W) 

w 
w 

A 

I 

U 
W 

U 
W 

A-I  Silicate 
W   Sulphate 

A 
A 

(W) 
A 

A 

(W) 
A 

A 
W 

A 
W 

A 
A 

A 

u 

w 
w 

A 
A 

w 
w 

W 
A 

A 
W 

A 

u 

A 
A 

Sulphide 
Sulphite 

A 

W 

(W) 

A 

(W) 

A 

U 

W3 

A 

w 

W 

(W) 

A 

(W)  Tartrate 
A 

Pb  Mgr 

Mn 

Hgi 

Hr* 

Ni 

Pt 

K 

Agr 

Na 

Sr 

Sn" 

Sn'- 

Zn 

1.  The  basic  salt  is  A.  6.  The  salt  is  soluble  in  water,  but  decomposed 

2.  The  acid  salt  is  W,  by   large  amounts,  insoluble  basic   com- 

3.  The  acid  salt  is  (W).  pounds  being  formed. 

4.  The  -ous  salt  is  A.  7.    Is  decomposed  by  boiling  with  water. 

5.  The -ous  salt  is  I.  8.    The  poly  sulphides  and  sulphydrates  are  (W). 


130  INSOLUBLE  SUBSTANCES.  [§§  89, 90. 

It  is  to  be  distinctly  borne  in  mind  that  this  table  is  not 
exhaustive,  and  is  intended  merely  as  a  help  to  the  begin- 
ner, who  is  analyzing  comparatively  simple  substances. 
In  the  case  of  complex  mixtures  the  table  is  of  little  ser- 
vice. Thus,  chloride  of  silver  is  designated  as  I,  but  it 
would  be  easy  to  mix  chloride  of  silver  and  chloride  of 
sodium  in  such  proportions  that  on  treatment  with  water 
the  whole  of  the  mixture  would  go  into  solution :  so  too  the 
chlorides  of  potassium  and  platinum  are  readily  soluble  in 
water,  each  by  itself,  but  the  double  chloride  of  these  two 
elements  is  so  insoluble  that  it  is  used  as  a  test  for  potas- 
sium (§  43). 

D.    Treatment  of  Insoluble  Substances. 

90.  The  substances  of  common  occurrence  which  are  prac- 
tically insoluble  in  water  and  acids  are :  — 

The  sulphates  of  barium,  strontium  and  lead.  Sometimes 
sulphate  of  calcium  occurs  in  difficultly  soluble  forms. 

Chloride  of  silver. 

The  anhydrous  sesquioxides  of  aluminum,  chromium  and 
iron,  either  native,  or  the  result  of  intense  ignition. 

Chrome-iron-ore,  a  native  mineral. 

Some  aluminates. 

Binoxide  of  tin,  native,  or  the  result  of  ignition. 

Silica  and  many  silicates. 

Fluoride  of  calcium  (fluor-spar). 

Beside  the  substances  included  in  this  list,  sulphur  and 
carbon,  or  graphite,  should,  perhaps,  be  mentioned,  because 
they  are  insoluble.  Bromide,  iodide  and  cyanide  of  silver 
are  decomposed  by  boiling  with  aqua  regia,  and  converted 
into  the  chloride,  so  that  these  substances  never  appear  in 
their  proper  form  in  the  final  insoluble  residue.  But  only 
in  case  aqua  regia  having  failed  to  dissolve  the  substance,  it 
is  directly  examined.     In  case  of  dealing  with  a  complex 


§§90,91.]  INSOLUBLE  SUBSTANCES.  131 

substance,  great  care  should  be  taken  that  all  soluble  material 
is  removed,  otherwise  many  complications  may  be  introduced. 

91.  Substances  which  resist  solution  in  liquids  are  gen- 
erally liquefied  by  the  action  of  fluxes  at  a  high  temperature ; 
they  are  fused  in  contact  with  some  powerful  decomposing 
agent,  like  the  carbonate  or  acid  sulphate  of  an  alkali  metal, 
or  the  hydrate  or  carbonate  of  an  alkaline -earth  metal.  Cer- 
tain preliminary  experiments  should  precede  the  fusion. 

The  insoluble  powder  is  first  examined  carefully  (with  the 
help  of  a  lens,  if  convenient)  to  ascertain  if  it  is  a  homo- 
geneous substance  of  the  same  color  throughout,  or  a  mixture 
composed  of  dissimilar,  variously  colored  particles.  The 
following  blowpipe  experiments  sometimes  give  decisive 
indications,  particularly  with  homogeneous  substances. 

a.  The  closed-tube  test  is  repeated,  looking  especially  for 
sulphur. 

b.  If  the  substance  is  black,  and  not  changed  by  heating 
in  the  closed  tube,  the  presence  of  carbon  in  some  form  is 
indicated.  Heat  a  small  sample  on  platinum  foil ;  if  it  is 
consumed,  carbon  is  present.  Graphite  is  not  consumed, 
but  can  be  recognized  by  its  property  of  soiling  the  fingers 
or  paper. 

c.  The  reduction  test  (§  83)  is  repeated  with  great  care, 
looking  especially  for  silver,  lead  and  tin,  and  applying  to 
the  globule,  if  any  is  obtained,  the  test  for  distinguishing 
between  these  three  white  metals.  This  test  has  already 
been  applied  to  the  original  substance ;  but  if  this  substance 
was  a  complex  mixture  containing  soluble  ingredients,  it 
is  quite  possible  that  the  test  should  give  a  more  satisfac- 
tory result,  now  that  all  substances  soluble  in  water  and 
acids  have  been  removed,  than  it  yielded  before.  If,  how- 
ever, decided  indications  of  the  presence  of  a  reducible 
metal  were  obtained  in  the  first  instance,  the  repetition  of 
the  test  is,  of  course,  unnecessary.  If  any  reducible  metal 
is  detected,  it  is  necessary  to  use  a  porcelain  crucible  for  the 


182  INSOLUBLE  SUBSTANCES.  [§  91. 

fusion  which  it  may  be  desirable  to  make  (§  92)  in  order 
to  convert  the  insoluble  substance  into  a  more  manageable 
form.  A  platinum  crucible  or  piece  of  platinum  foil,  which 
is  employed  for  most  fusions,  cannot  be  Used  with  safety 
when  the  substance  to  be  fused  contains  any  reducible 
mgtal ;  for  many  of  the  alloys  of  platinum  are  extremely 
fusible. 

d.  Prepare  another  pellet  of  a  mixture  of  equal  parts 
of  the  insoluble  powder  and  carbonate  of  sodium,  adding 
a  little  charocal  powder  to  the  paste.  Fuse  this  mixture 
upon  charcoal  in  the  reducing  flame  of  the  blowpipe.  Scoop 
out  the  fused  mass  and  the  surrounding  charcoal  with  a 
penknife,  place  the  dry  mass  -upon  a  bright  surface  of  silver 
(coin  or  foil),  and  wet  it  with  a  drop  of  water.  If  a  brown 
stain  be  produced  on  the  silver,  it  is  evidence  of  the  pres- 
ence of  sulphide  of  sodium  in  the  fused  mass.  This  sul- 
phide results  from  the  reduction  of  a  sulphate,  and  is 
evidence  of  the  presence  of  a  sulphate  in  the  substance 
tested.  The  odor  of  sulphuretted  hydrogen  is  often  per- 
ceptible when  the  fused  mass  is  moistened.  The  silver 
coin  or  foil  may  be  replaced  by  a  piece  of  lead  paper,  if  care 
be  taken  not  to  mistake  the  mere  dirtying  of  the  paper  for 
a  stain  of  sulphide;  the  silver  is,  however,  to  be  preferred; 
it  may  be  cleaned  after  use  by  treating  it  with  a  solution 
of  cyanide  of  potassium  and  then  washing  with  water.  It 
is  obvious  that  the  carbonate  of  sodium  used  in  this  test 
must  be  so  free  from  sulphate  of  sodium  as  not  itself  to 
give  this  reaction  on  silver,  after  fusion  on  charcoal.  Since 
coal  gas  invariably  contains  traces  of  sulphur  compounds, 
the  test  cannot  be  performed  with  a  gas  flame ;  a  candle  or 
lamp  flame  (App.,  §  82)  must  be  employed. 

It  is,  of  course,  possible  to  apply  this  test  for  sulphates 
to  the  fused  mass  obtained  in  (c) ;  this  second  test  is  in  fact 
unnecessary  when  a  decided  reaction  has  been  obtained  in 
the  first  instance. 


§  91.]  INSOLUBLE  SUBSTANCES.  133 

e.  Make  the  loop  on  the  end  of  the  bit  of  platinum  wire 
(App.,  §  83)  white-hot  in  the  blowpipe  flame,  and  thrust  it 
white-hot  into  some  powdered  borax ;  a  quantity  of  borax 
will  adhere  to  the  hot  wire ;  reheat  the  loop  in  the  oxidiz- 
ing flame ;  the  borax  will  puff  up  at  first,  and  then  fuse  to  a 
transparent  glass.  If  enough  borax  to  form  a  solid,  trans- 
parent bead  within  the  loop  does  not  adhere  to  the  hot  wire 
the  first  time,  the  hot  loop  may  be  dipped  a  second  time 
into  the  powdered  borax. 

When  a  transparent  glass  has  been  formed  within  the 
loop  of  the  platinum  wire,  touch  the  bead  of  glass  while  it 
is  hot  and  soft,  to  a  few  particles  of  the  insoluble  powder, 
and  reheat  the  bead  with  the  adhering  powder  in  the  oxi- 
dizing flame;  If  the  substance  dissolves  slowly  in  the 
borax,  and  the  bead  has  a  fine  yellowish-green  color  when 
cold,  chromium  is  probably  present.  Reheat  the  bead  in 
the  reducing  flame :  if  it  presents  a  bright  green  color  both 
when  hot  and  cold,  there  is  no  doubt  of  the  presence  of 
chromium. 

It  sometimes  happens  when  too  much  of  the  substance 
to  be  tested  has  been  added,  that  the  borax  bead  becomes 
so  dark  colored  as  to  be  practically  opaque.  It  may  then 
be  flattened  while  soft,  by  sudden  pressure  between  any 
smooth  metallic  surfaces,  like  the  flat  parts  of  jewellers' 
tweezers.  If  the  flattening  makes  the  color  of  the  borax 
glass  visible, -nothing  more  is  necessary;  but  if  the  glass 
is  still  too  dark,  all  the  glass  outside  the  loop  of  platinum 
may  be  broken  oif  by  gentle  hammering,  and  the  remaining 
glass  may  be  reheated  and  largely  diluted  by  the  addition 
of  more  borax. 

It  is  convenient  to  be  informed  of  the  presence  of  chro- 
mium, because  chromic  oxide  and  chrome  iron  ore  are  sub- 
stances which  it  is  particularly  difficult  to  decompose 
effectually  by  fusion.  In  presence  of  chromium,  no  other 
bead  reaction  which  can  be  anticipated  under  the  circum- 
stances will  give  a  decisive  result;  but  in  the  absence  of 


134     INSOLUBLE  SUBSTANCES.  —  FUSIONS.     [§§  91,  92. 

chromium,  the  presence  of  iron  may  be  determined.  A 
suitable  quantity  of  oxide  of  iron  causes  the  borax  bead, 
heated  in  the  oxidizing  flame,  to  look  red  when  hot  and 
yellow  when  cold.  In  the  reducing  flame  the  iron  bead 
becomes  greenish,  or  light  brownish-green. 

This  test  is  rendered  unnecessary  if  the  substance  under 
examination  be  a  white  powder,  or  if  from  other  appear- 
ances the  absence  of  chromium  is  assured. 

/.  The  test  for  fluorine  ( §  71)  should  be  applied  to  the 
original  substance,  if  it  has  not  already  been  done. 

When  all  the  above-mentioned  tests  (a-f)  give  negative 
results,  the  simplification  of  the  problem  is  very  conspicuous ; 
the  substances  which  may  be  present  are  reduced  to  alumina 
and  some  aluminates,  silica  and  silicates.  Again,  in  the 
case  of  a  substance  evidently  homogeneous,  if  the  prelimi- 
nary tests  give  aflirmative  results,  the  indications  of  the 
character  of  the  substance  are  almost  conclusive.  Thus 
chloride  of  silver,  sulphate  of  lead,  chromic  or  ferric  oxide, 
binoxide  of  tin,  or  fluoride  of  calcium,  may  be  satisfactorily 
identified  by  the  preliminary  tests  alone. 

There  are  two  methods  of  changing  insoluble  substances 
into  more  manageable  forms  by  the  application  of  heat  with 
sufficient  exactness  for  the  purposes  of  the  qualitative 
analyst,  —  the  method  of  fusion,  and  the  method  by  defla- 
gration. 

92.  Fusions.  —  Mix  the  fine  powder  of  the  insoluble  sub- 
stance with  about  six  parts  by  weight  of  dry  carbonate  of 
sodium  in  powder.  If  free  sulphur  is  present,  it  must  be 
first  removed  by  gentle  ignition  on  a  piece  of  porcelain. 
Both  powders  must  be  as  fine  as  they  can  be  made,  and 
they  must  be  intimately  mixed.  Keep  the  mixture  at  a 
bright  red  heat,  on  a  piece  of  platinum  foil  or  in  a  platinum 
crucible  (  a  porcelain  crucible,  if  a  reducible  metal  has  been 
found  in  the  substance,  §  91,  c,  and  fusion  is  for  any  reason 
preferred  to  deflagration  ),  until  the  mass  has  been  brought 


§§92,93.]     PUSlON   OF  INSOLUBLE  SUBSTANCES.      135 

to  a  state  of  quiet  fusion  (App.,  §  79).  Place  the  hot  plat- 
inum crucible,  when  withdrawn  from  the  lamp  or  fire,  on  a 
cold  block,  or  thick  plate  of  iron,  and  let  it  cool.  If  a  gas 
blast-lamp  be  employed,  the  supply  of  gas  may  be  inter- 
rupted, and  the  blast  of  air,  directed  as  before,  upbn  the 
crucible,  until  it  has  become  cold. 

When  the  green  borax  bead,  and  the  dark  color  of  the 
insoluble  powder,  point  to  the  presence  of  chrome  iron  ore, 
a  mixture  of  three  parts,  by  weight,  of  carbonate  of  sodium 
with  three  parts,  by  weight,  of  nitre,  may  be  substituted 
for  the  six  parts  of  carbonate  of  sodium  alone. 

93.  Treatment  of  the  Fused  Mass.  —  When  the  crucible 
has  been  cooled  in  the  way  mentioned  above,  the  fused  mass 
can  generally  be  removed  from  the  crucible  in  an  unbroken 
lump.  Soak  the  lump  in  boiling  water  until  everything  is 
dissolved  which  is  soluble  in  water.  If  the  mass  cannot  be 
detached  from  the  crucible,  the  crucible  and  its  contents 
must  be  soaked  in  boiling  water. 

The  aqueous  solution  of  the  fused  mass  is  filtered  from 
the  residue  insoluble  in  water  and  reserved.  That  portion 
of  the  fused  mass  which  boiling  water  did  not  dissolve  is 
treated  with  acid,  — hydrochloric  acid  if  silver  and  lead  be 
absent,  nitric  acid  if  either  of  these  metals  be  present,  — 
and  the  acid  solution  obtained  is  treated  as  will  be  de- 
scribed. If  a  portion  of  the  fused  mass  resist  both  water 
and  acids,  the  insoluble  portion  may  consist  of  separated 
silicic  acid,  or  of  some  of  the  original  substance  undecom- 
posed  by  the  fusion.  In  the  latter  case,  another  and  more 
prolonged  fusion  is  the  oiily  effectual  remedy,  although  it 
may  often  happen  that  a  partial  decomposition  of  the 
insoluble  substance  will  enable  the  analyst  to  recognize  all 
the  elements  which  it  contains. 

The  treatment  of  the  aqueous  and  acid  solutions  of  the 
last  paragraph  will  be  best  understood  if  we  first  consider 
what  changes  take  place  in  the  process  of  fusion.     Suppose 


136         FUSION  OF  INSOLUBLE  SUBSTANCES,       [§  93. 

that  the  substance  in  hand  is  sulphate  of  barium ;  at  the  high 
temperature  of  the  fusion  the  barium  and  sodium  change 
places  and,  instead  of  sulphate  of  barium  and  carbonate 
of  sodium,  there  result  carbonate  of  barium  and  sulphate 
of  sodium :  BaSO^  +  Na^COg  =  NagSO^  +  BaCOg.  When  the 
fused  mass  is  treated  with  water,  the  sulphate  of  sodium 
(with  the  excess  of  carbonate  of  sodium)  goes  into  solution, 
while  the  carbonate  of  barium,  which  is  insoluble  in  water, 
is  dissolved  by  the  hydrochloric  (or  nitric)  acid  as  chloride 
(or  nitrate)  of  barium.  Therefore  in  a  case  like  this,  the 
metallic  element  would  be  found  in  the  acid  solution  and 
the  class  or  kind  of  salt  might  be  determined  by  applying 
the  test  for  sulphates  to  the  aqueous  solution.  Again,  sup- 
pose the  substance  under  examination  is  a  double  silicate 
of  calcium  and  aluminum.  After  fusion  with  carbonate  of 
sodium  and  treatment  successively  with  water  and  acid,  a 
portion  of  the  silicic  acid  will  be  in  the  aqueous  solution 
(as  silicate  of  sodium)  and  a  portion  in  the  acid  solution, 
while  a  part  may  remain  insoluble ;  the  aluminum  will  ex- 
ist partly  in  the  aqueous  solution  (as  aluminate  of  sodium) 
and  partly  in  the  acid  solution  (as  chloride  of  aluminum) ; 
the  calcium,  which  after  the  fusion  remained  as  car- 
bonate, insoluble  in  water,  will  have  been  converted  into 
chloride  and  will  be  found  in  the  acid  solution.  Having 
considered  the  general  nature  of  the  changes  brought  about 
by  fusion  with  carbonate  of  sodium,  we  proceed  to  the  state- 
ment of  the  treatment  of  the  aqueous  and  acid  solutions  of 
the  fused  mass. 

a.  If  the  test  for  sulphates  described  in  §  91,  d,  on  page 
132,  has  failed  to  give  satisfactory  indications,  acidify  a 
small  portion  of  the  aqueous  solution  with  hydrochloric 
acid,  and  apply  the  barium  test.  The  carbonate  of  sodium 
used  in  the  fusion  should  be  free  from  sulphate. 

6.  Acidify  another  small  portion  with  acetic  acid,  and 
apply  the  lead  test  for  chromates  (§  63).     In  presence  of 


§  93.]        FUSION  OF  INSOLUBLE  SUBSTANCES.         137 

sulphuric  acid  this  test  will  be  obscured,  but  not  rendered 
wholly  useless  (§  31,  p.  49). 

c.  Acidify  a  third  portion  with  nitric  acid,  and  apply 
the  silver  test  for  chlorine.  The  student  must  first  prove 
that  his  carbonate  of  sodium  contains  no  chloride. 

d.  If  the  test  for  fluorine  by  the  method  of  §  71  has  for 
any  reason  been  unsatisfactory,  a  fourth  portion,  having 
been  concentrated  by  evaporation  in  a  porcelain  dish,  and 
again  cooled,  is  acidified  with  hydrochloric  acid,  and  then 
left  at  rest  until  the  carbonic  acid  has  escaped.  It  is  then 
supersaturated  with  ammonia,  heated,  and  filtered  while 
hot.  The  filtrate  is  collected  in  a  bottle;  chloride  of  cal- 
cium is  immediately  added  to  it;  the  bottle  is  closed  and 
allowed  to  stand  at  rest.  If  the  original  substance  con- 
tained a  fluoride,  the  fluorine  will  have  combined  with 
sodium  during  the  fusion,  and  fluoride  of  sodium  will  be 
contained  in  the  aqueous  solution.  The  carbonic  acid  hav- 
ing been  expelled,  and  all  substances  precipitable  by  ammo- 
nia having  been  removed,  the  chloride  of  calcium  will  throw 
down  the  fluoride  of  calcium.  If  a  precipitate  separates  from 
the  liquid  in  the  bottle  after  some  time,  it  is  collected  in  a 
small  filter,  dried  and  examined  for  fluorine  by  the  method 
of  §  71. 

When  the  tests  a-d  give  negative  results,  or  when  by  pre- 
vious tests  the  absence  of  sulphates,  chromates,  chlorides 
and  fluorides  is  made  certain,  the  remainder  of  the  aqueous 
solution  is  added  to  the  acid  solution  and  the  mixture  is 
evaporated  to  dryness  and  ignited;  the  residue  thus  ob- 
tained is  boiled  with  dilute  hydrochloric  (or  nitric)  acid. 
If  the  dilute  acid  fails  to  dissolve  the  residue  completely, 
tlie  insoluble  portion  consists  of  silicic  acid.  The  solution  is 
examined  in  the  usual  way  for  the  metallic  elements  (§  45), 
except,  of  course,  sodium  (and  sometimes  potassium),  which 
has  been  added  in  the  flux.     (See  §  94,  p.  139.) 

When  the  preliminary  examination  or  the  tests  a-d  show 


138  FUSION   OF  INSOLUBLE  SUBSTANCES.         [§93. 

the  presence  of  one  or  more  of  the  classes  of  salts  men- 
tioned above,  the  treatment  is  slightly  different.  In  that 
case  the  remainder  of  the  aqueous  solution  is  acidified  with 
hydrochloric  acid,  evaporated  to  dryness  and  ignited;  the 
residue  thus  obtained  is  boiled  with  dilute  hydrochloric 
acid.  If  the  acid  fails  to  dissolve  the  residue  completely, 
the  insoluble  portion  consists  of  silica;  the  solution  may 
be  tested  for  aluminum.  (See  p.  136.)  If  silicic  acid  has 
been  found  in  the  aqueous  solution,  the  original  acid  solu- 
tion of  the  fused  mass  is  evaporated  to  dryness  and  ignited ; 
the  residue  is  treated  with  dilute  acid,  and  the  solution, 
after  being  filtered  from  the  silicic  acid,  is  examined  for  the 
metallic  elements  in  the  usual  manner.  It  is  evidently  im- 
practicable in  this  last  case  to  mix  the  aqueous  and  the  acid 
solutions,  for  if  the  case  of  sulphate  of  barium  (p.  136)  be 
taken  as  an  example,  in  mixing  the  aqueous  solution  (con- 
taining sulphate  of  sodium)  and  the  acid  solution  (contain- 
ing chloride  of  barium),  there  would  be  an  immediate 
precipitation  of  the  insoluble  sulphate  of  barium,  which 
was  the  substance  to  be  analyzed. 

Silicates  are  by  far  the  most  common  of  insoluble  sub- 
stances.  A  great  variety  of  metallic  elements  occur  in 
insoluble  silicious  minerals,  so  that  the  possible  contents  of 
the  acid  solution  of  the  fused  mass  are  very  various.  The 
evaporation  to  dryness  in  order  to  render  the  silica  insoluble 
is  prescribed  because  the  subsequent  examination  goes  on 
the  better  for  this  preliminary  removal  of  silica,  which,  if 
left  in  solution,  might  create  confusion  by  appearing  as  a 
precipitate  at  almost  any  stage  of  the  analysis. 

Many  silicates  contain  sodium  and  potassium.  When  the 
presence  or  absence  of  these  alkali  metals  is  to  be  deter- 
mined, it  is  evident  that  the  pulverized  silicate  must  not  be 
fused  with  carbonate  of  sodium,  but  with  some  decomposing 
flux  free  from  alkali. 


§§94-96.]  INSOLUBLE  SUBSTANCES.  139 

94.  Decomposition  by  Means  of  Carbonate  of  Calcium  and 
Chloride  of  Ammonium.  —  An  intimate  mixture  is  prepared 
of  one  part  of  the  silicate,  six  parts  of  pure  precipitated 
carbonate  of  calcium,  three  fourths  part  of  pulverized  chlo- 
ride of  ammonium.  This  mixture  is  heated  to  bright  redness 
in  a  platinum  crucible  for  thirty  or  forty  minutes.  The 
crucible  with  its  contents  (which  should  be  in  a  coherent, 
sintered,  but  not  thoroughly  fused  condition)  is  then  placed 
in  a  beaker,  and  soaked  for  half  an  hour  in  water  kept  near 
the  boiling  point.  The  contents  of  the  beaker  are  then 
filtered.  The  filtrate,  containing  caustic  lime,  chloride  of 
calcium  and  all  the  sodium  and  potassium  of  the  original 
silicate  as  chlorides,  is  treated  with  a  little  ammonia-water, 
and  with  carbonate  of  ammonium  in  slight  excess ;  the  liq- 
uid is  heated  to  boiling  and  filtered.  This  second  filtrate 
is  evaporated  to  dryness,  and  gently  ignited  to  expel  the 
ammonium  salts.  The  residue  is  dissolved  in  a  little  water; 
one  or  two  drops  of  carbonate  of  ammonium  and  a  drop  of 
oxalate  of  ammonium  are  then  added ;  the  mixture  is  again 
heated  and  filtered ;  this  third  filtrate  is  evaporated  to  dry- 
ness and  ignited;  the  ignited  residue,  if  there  be  any,  con- 
sists of  the  chlorides  of  sodium  and  potassium,  or  of  one  of 
these  two  salts.    This  residue  is  examined  according  to  §  43. 

95.  Fusion  with  Acid  Sulphate  of  Sodium.  —  The  fol- 
lowing method  may  be  tried  to  advantage  upon  ferric  oxide, 
chromic  oxide  or  chrome  iron  ore,  and  some  very  refractory 
silicates.  Heat  the  insoluble  substance  with  three  or  four 
times  its  bulk  of  acid  sulphate  of  sodium  (App.,  §  30)  in  a 
platinum  crucible,  until  the  sulphate  melts ;  then  maintain 
it  in  the  liquid  state  for  half  an  hour.  This  operation 
should  be  performed  under  a  hood.  The  fused  mass  is 
treated  essentially  as  before  (§  93),  allowance  being  made 
for  the  different  nature  of  the  flux. 

96.  Deflagration.  —  The  method  of  fusion  just  described 
involves  the  use  of  a  platinum  or  porcelain  crucible,  and 


140  DEFLA  GRA  TION. 

demands  the  heat  of  a  blast-lamp,  or  strong  coal  fire.  Nei- 
ther crucibles,  lamps  nor  fires  are  necessary  in  the  method 
of  deflagration  which  applies  the  heat  inside  the  mass  to 
be  fused.  This  decomposition  by  deflagration  is  performed 
as  follows :  —  One  part,  by  weight,  of  the  insoluble  powder 
is  intimately  mixed  with  two  parts  of  dry  carbonate  of  so- 
dium, two  parts  of  fine  and  pure  charcoal  powder  and  twelve 
parts  of  powdered  nitre.  The  mixture  is  put  in  a  thin  por- 
celain dish  or  clean  iron  tray;  the  dish,  or  little  tray,  is 
placed  under  a  hood,  or  in  the  open  air,  and  a  lighted  match 
is  applied  to  the  centre  of  the  heap.  The  deflagration  is 
completed  in  two  or  three  seconds,  and  a  well-fused  mass 
remains.  This  mass  is  detached  from  the  cooled  dish  or 
traj',  and  boiled  with  water  in  a  beaker ;  it  is  generally  very 
porous,  and  is  therefore  readily  disintegrated  by  stirring  it 
in  the  hot  water  with  a  glass  rod.  The  soluble  portion  will 
all  be  extracted  in  a  very  few  minutes.  The  residue  left  by 
water  is  treated  with  acid  precisely  as  described  in  §  93. 
The  aqueous  and  acid  solutions  of  the  deflagrated  sub- 
stance are  submitted  to  the  same  operations  as  the  corre- 
sponding solutions  of  substances  fused  in  crucibles.  A 
little  charcoal  is  generally  left  undissolved  by  the  acid, 
and  with  it  any  of  the  substance  which  may  have  escaped 
decomposition.  The  mixture  of  one  part,  by  weight,  of 
powdered  charcoal,  and  six  parts  of  nitre,  may  be  kept  ready 
mixed  for  effecting  the  fusion  of  insoluble  substances. 

The  advantages  of  this  process  are  that  it  is  quick,  re- 
quires only  cheap  and  common  tools,  and  may  be  applied  to 
substances  containing  reducible  metals,  as  well  as  to  any 
others.  It  is,  of  course,  inapplicable  when  sodium  and 
potassium  are  to  be  sought  for  in  silicates.  Chrome  iron 
ore  cannot  be  decomposed  in  this  way.  The  insoluble 
sulphates,  chloride  of  silver,  binoxide  of  tin,  fluor-spar, 
glass,  and  many  natural  silicates,  may  be  very  well  treated 
by  this  method,  in  spite  of  its  apparent  roughness. 


CHAPTER  XII. 

TREATMENT  OF  A  PURE  METAL  OR  ALLOY. 

97.  The  elements  which  are  now  used  in  the  arts  in  the 
metallic  state,  and  which  therefore  may  come  into  the  hands 
of  the  analyst  as  metals,  either  pure  or  alloyed,  are  silver, 
lead,  mercury,  bismuth,  cadmium,  copper,  arsenic,  anti- 
mony, tin,  gold,  platinum,  aluminum,  iron,  zinc,  nickel, 
manganese  and  magnesium.  These  metals  can  all  be  brought 
into  solution  and  detected  in  the  wet  way  with  ease  and 
certainty.  It  is  therefore  not  worth  while  to  submit  a 
metal,  or  metallic  alloy,  to  preliminary  blowpipe  tests,  al- 
though at  need  mercury  and  arsenic  can  be  readily  detected 
by  the  closed-tube  test  (§  82),  and  many  others,  by  exposing 
them  on  charcoal  to  the  reducing  and  oxidizing  flame  (com- 
pare §  83,  pp.  112-115). 

A  portion  of  the  metal  or  alloy  to  be  examined  should 
first  be  reduced  to  as  fine  a  state  of  division  as  possible. 
If  it  is  brittle,  it  can  be  powdered;  if  soft,  shavings  can 
be  cut  from  it;  if  tough  and  hard,  it  can  perhaps  be  fused, 
and  shaken  into  powder  while  melted,  or  granulated  by 
being  poured  from  a  height  into  cold  water.  Filings  should 
be  the  last  resort,  because  of  the  possibility  of  foreign 
admixture  of  iron. 

98.  Action  of  Nitric  Acid  on  the  Metals.  —  A  small  quan- 
tity of  the  divided  metal  or  alloy,  about  the  equivalent  of 
a  pea  in  bulk,  is  placed  in  a  flask,  covered  with  concentrated 
nitric  acid,  and  heated  gently  under  a  hood  or  in  the  open 
air  for  half  an  hour  or  until  no  further  change  is  noticed 
on  the  addition  of  more  concentrated  nitric  acid. 

141 


142  TREATMENT  OF  ALLOYS.  [§  98. 

If  complete  solution  ensues,  gold,  platinum,  tin  and  anti- 
mony are  probably  altogether  absent;  they  can  only  be 
present  in  very  minute  proportion.  Any  of  the  other  metals 
above  enumerated  may  be  present.  Transfer  the  acid  solu- 
tion to  a  porcelain  dish,  and  evaporate  it  almost  to  dryness 
to  drive  off  the  free  acid;  dilute  the  evaporated  liquid  with 
about  ten  times  its  bulk  of  water,  and  proceed  with  the 
analysis  in  the  usual  way  (§  45).  If  the  solution,  from 
which  the  greater  part  of  the  free  acid  has  been  removed 
by  evaporation,  becomes  turbid  on  the  addition  of  water, 
bismuth  is  doubtless  present.  In  this  case  enough  acid  must 
be  restored  to  the  solution  to  clarify  it.  Mercury,  if  pres- 
ent, will  be  dissolved  to  mercuric  nitrate. 

If  a  residue  remains  undissolved,  add  a  little  more  acid  to 
make  sure  that  the  acid  is  incapable  of  further  action;  and 
when  this  point  is  settled,  test  a  drop  or  two  of  the  clear 
liquid  on  platinum  foil,  to  ascertain  if  anything  has  entered 
into  solution.  If  the  nitric  acid  has  effected  a  partial  solu- 
tion of  the  original  metal,  evaporate  the  liquid  nearly  to 
dryness,  dilute  the  evaporated  mixture  with  water,  filter, 
and  submit  the  filtrate  to  the  usual  course  of  analysis.  The 
residue  is  thoroughly  washed  with  water,  to  prepare  it  for 
further  treatment.  On  diluting  the  evaporated  mixture  with 
water,  a  turbidity  due  to  the  presence  of  bismuth  may 
appear.  The  experienced  operator  will  hardly  fail  to  dis- 
tinguish between  any  such  turbidity  and  a  residue  insoluble 
in  the  nitric  acid.  To  avoid  mistakes  which  would  lead  to 
the  unnecessary  addition  of  acid,  it  is  well  to  take  out  a  drop 
of  the  nitric  acid  solution  before  evaporation  and  to  add 
it  to  several  teaspoonfuls  of  water  contained  in  a  test- 
tube.  (See  p.  26.)  The  absence  or  presence  of  bismuth  will 
thus  be  discovered.  It  will  sometimes  happen  that  a  white 
residue  appears  in  the  nitric  acid  solution  which  disappears 
when  the  evaporated  mixture  is  diluted.  This  is  owing  to 
the  presence  of  lead:  nitrate  of  lead  is  rather  insoluble  in 


§  98.]  TREATMENT  OF  ALLOYS.  143 

stong  nitric  acid,  but  passes  into  solution  readily  when  the 
mixture  is  diluted. 

Three  different  cases  of  insoluble  residues  may  occur, 
readily  distinguished  by  the  mere  appearance  of  the  residue. 

a.  The  insoluble  substance  is  non-metallic  and  white. 
In  this  case  tin  and  antimony  may  be  present,  but  gold  and 
platinum  are  probably  absent.  The  white  residue  may  con- 
tain the  insoluble  oxides  of  tin  and  antimony,  or  either  of 
them.  These  elements  are  to  be  detected  by  the  methods 
of  §  25. 

b.  The  insoluble  substance  is  metallic,  as  evidenced  by 
its  lustre,  if  it  is  in  visible  fragments,  or  by  the  weight  and 
gray  or  black  color  of  its  powder,  if  it  is  in  a  fine  state  of 
division.  Such  a  residue  must  be  either  gold  or  platinum 
(or  some  of  the  rare  platinum-like  metals  which  lie  without 
the  range  of  this  manual).  The  residue  is  dissolved  in 
aqua  regia,  and  evaporated  to  a  very  small  bulk. 

Test  for  Gold.  —  A  portion  of  this  evaporated  liquid  is 
diluted  with  ten  times  its  bulk  of  water,  and  poured  into  a 
beaker  which  is  placed  on  a  sheet  of  white  paper.     A  small 
quantity  of  a  solution  of  stannous  chloride  is  tinged  yellow 
by  the  addition  of  a  few  drops  of  solution  of  ferric  chloride 
(App.,  §  49),  and  is  then  considerably  diluted.    A  glass  rod 
is  dipped,  first  into  this  tin  solution,  and  then  into  the  so- 
lution to  be  tested  for  gold.    If  even  a  trace  of  the     xest 
precious  metal  be  present,  a  blue  or  purple  streak      for 
will  be  observed  in  the  track  of  the  rod.     If  the      •^^• 
quantity  of  gold  be  more  considerable,  a  pink  tinge  will  be 
imparted  to  the  solution,  or  a  purplish  precipitate  will  be 
produced  by  a  sufficient  quantity  of  the  tin  solution.     This 
^'  purple-of-Cassius  "  test  is  applicable  to  very  acid  solutions. 

Test  for  Platinum.  —  To  another  undiluted  por-  Test 
tion  of  the  cooled  aqua  regia  solution,  a  cold  for 
concentrated  solution  of  chloride  of  ammonium  P*- 
is  added.     The  formation  of  a  yellow,  crystalline  precipi- 


144  TBEATMENT  OF  ALLOYS. 

tate  of  chloroplatinate  of  ammonium  indicates  the  presence 
of  platinum  (or  of  some  rare  platinum-like  metal).  By 
adding  a  little  alcohol  to  the  liquid,  the  test  is  made  more 
delicate.  In  a  difficult  case,  the  aqua  regia  solution  might 
be  evaporated  to  dryness  with  chloride  of  ammonium,  and 
the  residue  treated  with  weak  alcohol  and  water,  which 
would  dissolve  all  the  ingredients  except  the  chloroplat- 
inate. Upon  ignition,  chloroplatinate  of  ammonium  leaves 
spongy  platinum  behind. 

It  happens  exceptionally  in  the  case  of  certain  alloys, 
especially  in  the  presence  of  copper,  that  concentrated^  nitric 
acid  fails  to  attack  them  even  when  it  is  hot;  it  is  well, 
therefore,  before  inferring  the  presence  of  an  insoluble 
metallic  residue,  to  try  the  effect  of  boiling  the  seemingly 
insoluble  substance  in  nitric  acid  diluted  with  an  equal  bulk 
of  water. 

c.  The  insoluble  residue  contains  both  a  white  powder 
and  a  metallic  substance.  It  must  then  be  examined  for 
antimony,  tin,  gold  and  platinum  precisely  as  described  in 
§25. 


CHAPTER  XIII. 

TREATMENT  OP  LIQUIDS. 

99.  Evaporation  Test.  —  The  first  step  in  the  examina- 
tion of  an  unknown  liquid  is  to  evaporate  a  few  drops  at 
a  gentle  heat  on  platinum  foil.  Attention  should  be  paid 
to  the  smell  of  the  escaping  vapors  in  order  to  ascertain  if 
the  solvent  be  water  or  some  other  fluid,  like  alcohol,  ether, 
benzine  or  a  strong  acid.  If  no  appreciable  residue  remain, 
the  fluid  is  probably  pure  water,  or  some  other  volatile  liq- 
uid; or  it  is  possible  that  the  liquid  is  some  very  dilute 
solution,  like  a  spring  water,  which  needs  extreme  concen- 
tration before  the  solid  substances  dissolved  in  it  can  be 
detected.  When  a  residue  remains  on  the  foil,  the  heat  is 
increased :  first,  to  ascertain  if  the  dissolved  substances  are 
wholly  volatile,  in  which  case  only  compounds  of  ammo- 
nium, mercury,  arsenic  and  antimony  can  be  present;  and 
secondly,  to  ascertain  if  there  be  any  organic  matter  in  the 
liquid.  Carbonization  or  charring  with  the  attendant  phe- 
nomena (§  82, 1)  occurs  when  fixed  organic  matter  is  present. 
If  organic  matter  is  discovered,  it  must  be  destroyed  by 
the  second  method  of  §  84,  before  the  analysis  can  be  pro- 
ceeded with.  A  volatile  organic  solvent  can,  of  course,  be 
got  rid  of  by  a  simple  evaporation  to  dryness. 

100.  Testing  with  Litmus.  —  The  next  step  is  to  test  the 
solution  with  litmus  paper. 

a.    If  it  is  neutral,  and  the  solvent  is  water,  consult  §  88. 

6.  If  it  is  acid,  the  acidity  may  be  due  to  a  normal  salt 
having  an  acid  reaction,  or  to  an  acid  salt  or  to  free  acid. 
No  general  inferences  can  be  drawn  from  the  acid  reaction, 

146 


146  TBEATMENT  OF  LIQUIDS. 

except  that  carbonates  and  sulphides  are  absent.     If  dilu- 
tion of  the  acid  fluid  produces  turbidity,  the  presence  of 
antimony  or  bismuth  may  be  inferred, 
c.    If  it  is  alkaline,  consult  §  88,  I,  c. 

101.  By  evaporating  a  portion  of  the  original  solution  to 
dryness,  the  dissolved  solid  is  obtained.  This  solid  may 
be  subjected  to  the  whole  of  the  preliminary  treatment 
prescribed  for  a  salt,  mineral  or  other  non-metallic  solid 
(§§  82,  83) ;  but  inasmuch  as  the  main  object  of  all  prelimi- 
nary treatment  of  a  solid  is  to  learn  how  to  get  it  into  solu- 
tion with  the  least  difiiculty,  it  is  seldom  worth  while  for  the 
analyst  to  make  a  solid  out  of  a  solution,  and  thus  forego 
the  advantage  of  having  the  solution  already  made  to  his 
hand. 

102.  Testing  for  Ammonia.  —  A  small  portion  of  the  orig- 
inal solution  must  always  be  tested  for  ammonium  salts  by 
heating  it  in  a  test-tube  with  an  equal  bulk  of  slaked  lime.jrK^ 
The  gas  is  recognized  by  its  smell  and  its  reaction  with 
hydrochloric  acid  (§  82,  II,  h),  <^    '^^rA-'  t^A^^^^r^^^'^  \.tjv,^ 


The  means  of  identifying  and  isolating  the  rare  elements, 
the  methods  by  which  minute  traces  of  one  substance  may 
be  detected  when  hidden  in  proportionally  large  quantities 
of  other  substances,  as  when  the  impurities  of  chemicals  and 
drugs  are  exhibited,  and  the  processes  to  be  employed  in 
special  cases  of  peculiar  difficulty,  such  as  the  analysis  of 
complex  insoluble  minerals,  or  the  detection  of  mineral  poi- 
sons in  masses  of  organic  matter,  must  be  studied  in  complete 
treatises  upon  chemical  analysis,  or  in  works  specially 
devoted  to  these  technical  matters.  Such  details,  however 
valuable  to  the  pi-ofessional  analyst,  or  expert,  would  not 
be  in  harmony  with  the  plan  of  this  manual. 


APPENDIX. 


APPENDIX, 


REAGENTS. 

[Those  reagents  in  the  following  list  which  are  used  in  considerable 
quantities  are  marked  with  an  asterisk  (*).] 

The  ordinary  commercial  substances  are,  as  a  rule,  sufficiently 
pure  for  the  purposes  of  this  manual.  If  in  any  experiment  doubts 
arise  as  to  the  character  of  a  reagent,  a  quantity  of  it  somewhat 
larger  than  that  which  has  been  mixed  with  the  substance  under  ex- 
amination should  be  tested  by  itself,  and  the  reaction  compared  with 
that  exhibited  in  the  doubtful  case.  If  the  result  of  this  trial  is  unsat- 
isfactory, the  experiment  must  be  repeated  with  reagents  which  are 
known  to  be  pure. 

1.  *  Hydrochloric  Acid  (Concentrated).  —  The  strong,  com- 
mon acid  prepared  by  chemical  manufacturers,  though  usually  far 
from  pure,  will  answer  for  most  of  the  purposes  of  this  manual.  It 
must,  however,  be  continually  borne  in  mind  that  the  commercial  acid 
is  usually  contaminated  with  sulphuric  acid,  and  very  often  with  traces 
of  arsenic  and  iron.  These  impurities  may  be  present  in  sufficient 
quantity  to  render  the  acid  unfit  for  use  when  these  very  substances 
are  to  be  tested  for  in  the  mixture  to  be  analyzed. 

The  yellow  color  of  the  commercial  acid,  though  often  attributed 
to  iron,  is  really  due  for  the  most  part  to  the  presence  of  a  peculiar 
organic  compound  which  is  soluble  in  the  strong  acid. 

2.  Hydrochloric  Acid  (Pure). 

3.  *  Hydrochloric  Acid  (Dilute). —  Mix  1  volume  of  the  com- 
mon concentrated  acid,  or  —  where  special  purity  is  required  —  of  the 
pure  strong  acid,  with  4  volumes  of  water. 

149 


150  BE  AGENTS.  [§§  4-13. 

4.  *  Nitric  Acid  (Concentrated). —  Use  the  colorless  commer- 
cial acid  of  1.38  or  1.40  specific  gravity.  Strong  nitric  acid  of  tolerable 
purity  can  be  obtained  from  the  dealers  in  coarse  chemicals.  An  acid 
which,  when  diluted  with  5  parts  of  water,  gives  no  decided  cloudi- 
ness with  either  nitrate  of  silver  (absence  of  hydrochloric  acid)  or 
nitrate  of  barium  (absence  of  sulphuric  acid)  is  good  enough  for  most 
uses  in  qualitative  analysis. 

5.  Nitric  Acid  (Pure). 

6.  *  Nitric  Acid  (Dilute).  —  Mix  1  volume  of  the  strong  acid  with 
5  volumes  of  water. 

7.  Aqua  regia  should  be  prepared  only  in  small  quantities,  at 
the  moment  of  use,  by  mixing  in  a  test-tube  1  volume  of  strong 
nitric  acid  with  3  or  4  times  as  much  strong  hydrochloric  acid. 

8.  *  Sulphuric  Acid  (Concentrated).  —  The  oil  of  vitriol  of 
commerce  will  usually  be  found  pure  enough  for  the  purposes  of  this 
manual. 

9.  Sulphuric  Acid  (Pure). —  Sulphuric  acid  free  from  hydro- 
chloric acid  is  necessary  in  testing  for  chlorine,  according  to  §  72. 
Such  acid  may  be  obtained  from  the  dealers  in  chemicals,  but  acid 
purporting  to  be  pure  should  invariably  be  tested  by  diluting  a  portion 
with  a  considerable  quantity  of  water  and  adding  a  few  drops  of 
nitrate  of  silver.  No  turbidity  should  appear  after  the  mixture  has 
stood  for  some  time. 

10.  *  Sulphuric  Acid  (Dilute)  is  prepared  by  gradually  adding 
1  part  by  measure  of  the  concentrated  acid  to  4  parts  of  water  con- 
tained in  a  beaker  or  porcelain  dish ;  the  mixture  must  be  constantly 
stirred  with  a  glass  rod.  When  the  mixing  is  finished,  the  liquid  is 
left  at  rest  until  all  the  sulphate  of  lead,  which  has  separated  from  the 
strong  acid,  has  settled  to  the  bottom  ;  the  clear  liquid  is  then  decanted 
into  bottles. 

11.  Sulphuric  Acid  (Dilute).  — Mix,  as  described  in  the  pre- 
ceding section,  1  part  of  the  strong  acid  with  6  parts  of  water. 

12.  Oxalic  Acid. — Dissolve  1  part,  by  weight,  of  the  commer- 
cial crystals  in  20  parts  of  water. 

13.  *  Acetic  Acid.  —  The  ordinary  commercial  acid ;  or  dilute 
Glacial  acetic  acid  with  two  and  a  half  times  its  own  volume  of 
water. 


§§14-18.]  BEAGENTS.  151 

14.  Tartaric  Acid  should  be  kept  in  the  state  of  powder,  since 
solutions  of  it  slowly  decompose.  For  use,  dissolve  a  small  portion  of 
the  powder  in  2  or  3  times  its  volume  of  hot  water. 

15.  *  Sulphuretted  Hydrogen  Gas  (Sulphydric  Acid)  is  pre- 
pared as  needed,  by  acting  upon  fragments  of  sulphide  of  iron  with 
dilute  sulphuric  acid  in  the  apparatus  described  in  §§  93,  94,  of  this 
Appendix.  The  apparatus  should  always  be  placed  either  in  the  open 
air  or  in  a  strong  draught  beneath  a  chimney. 

16.  Sulphuretted  Hydrogen  "Water.  —  Pass  sulphuretted  hydro- 
gen gas  into  a  bottle  of  water  until  the  water  can  absorb  no  more. 
To  determine  when  the  absorption  is  complete,  close  the  mouth  of  the 
bottle  tightly  with  the  thumb,  and  shake  the  liquid.  If  the  water  is 
saturated,  a  small  portion  of  the  gas  will  be  set  free  by  the  agitation, 
and  a  slight  outward  pressure  against  the  thumb  will  be  felt.  If  the 
water  is  not  fully  saturated,  the  agitation  will  enable  it  to  absorb  the 
gas  which  lay  in  the  upper  part  of  the  bottle,  and  a  partial  vacuum 
will  be  created,  so  that  an  inward  pressure  will  be  felt. 

Since  sulphuretted  hydrogen  water  soon  decomposes  when  exposed 
to  the  air,  it  should  always  be  kept  in  tightly  closed  bottles,  and  no 
very  large  quantity  of  it  should  be  prepared  at  once.  A  good  way  of 
keeping  the  solution  is  to  fill  a  number  of  small  phials  with  the  fresh 
liquid,  cork  them  tightly,  and  invert  them  in  water,  so  that  their  necks 
shall  always  be  immersed  and  protected  from  the  atmosphere. 

At  the  moment  of  using  this  reagent  its  quality  should  always  be 
proved  by  smelling  of  it,  or  by  adding  a  drop  or  two  of  the  liquid  to 
a  drop  of  acetate  of  lead,  which  should  be  immediately  blackened 
from  the  formation  of  sulphide  of  lead. 

17.  *  Ammonia- Water.  —  Commercial  aqua-ammoniae  may  usu- 
ally be  obtained  pure  enough  for  the  purposes  of  this  manual.  Dilute 
1  volume  of  the  strong  liquor  with  3  volumes  of  water.  Ammonia- 
water  should  be  free  from  carbonic  acid ;  when  diluted,  as  above,  it 
ought  not  to  yield  any  precipitate  when  tested  with  lime-water. 

18.  *  Sulphide  of  Ammonium.  —  Pass  sulphuretted  hydrogen 
gas  through  ammonia-water,  diluted  as  described  in  §  17,  until  a  por- 
tion of  the  liquid  yields  no  precipitate  when  tested  with  a  drop  of  a 
solution  of  sulphate  of  magnesium  (absence  of  free  ammonia). 

Since  sulphide  of  ammonium  decomposes  after  a  while,  when 
exposed  to  the  air,  it  is  not  advisable  to  prepare  it  in  large  quantities. 
In  case  any  doubt  arise  as  to  the  quality  of  the  reagent,  add  some  of 


152  BEAGENTS.  [§§  19-23. 

it  to  a  drop  of  acetate  of  lead.  Unless  a  dense  "black  precipitate 
of  sulphide  of  lead  is  immediately  thrown  down,  the  sulphide  of 
ammonium  is  worthless.  The  sulphide  as  prepared  above,  if  allowed 
to  stand  for  some  time  exposed  to  light,  usually  becomes  sufficiently 
transformed  to  the  yellow  sulphide  for  use.  But  yellow  sulphide  of 
ammonium  may  be  prepared  directly  by  dissolving  sulphur  to  satura- 
tion in  the  above-mentioned  solution. 

19.  *  Carbonate  of  Ammonium.  —  Dissolve  without  warming 
1  part,  by  weight,  of  the  commercial  salt,  in  4  parts  of  water,  and  add 
to  the  mixture  1  part  of  strong  ammonia-water. 

The  solution  of  carbonate  of  ammonium  should  be  kept  in  bottles 
made  of  glass  which  is  free  from  lead.  If  kept  in  flint-glass  bottles, 
the  carbonate  of  ammonium  takes  up  some  lead  so  that  when,  in  pre- 
cipitating the  carbonates  of  Class  VI,  this  reagent  is  added  to  a  solu- 
tion containing  sulphide  of  ammonium,  a  dark  coloration  appears  in 
the  liquid  or  obscures  the  precipitate,  to  the  annoyance  of  the  operator. 

20.  *  Chloride  of  Ammonium.  —  Dissolve  without  warming  1 
part,  by  weight,  of  the  crystallized  commercial  salt  in  10  parts  of 
water ;  let  the  solution  stand  for  a  day  or  so  and  then  filter  it. 

21.  *  Oxalate  of  Ammonium.  —  Dissolve  1  part,  by  weight,  of 
the  salt  in  24  parts  of  water ;  or,  dissolve  37  grms.  of  crystallized 
oxalic  acid  in  450  cubic  centimetres  of  water,  neutralize  exactly  with 
ammonia-water  and  dilute  to  the  bulk  of  1  litre. 

22.  Molybdate  of  Ammonium.  —  Dissolve  1  part  of  molybdic 
acid  in  4  parts  of  strong  ammonia-water,  taking  care  to  add  only  a 
little  molybdic  acid  at  a  time,  and  to  stir  after  each  addition.  Filter 
the  ammoniacal  solution  and  allow  it  to  cool.  Mix  the  clear  solution 
with  15  parts  of  strong  nitric  acid,  adding  the  ammonia  solution 
slowly,  with  constant  stirring,  taking  care  to  keep  the  mixture  cool. 
Let  the  mixture  stand  24  hours  in  a  warm  place  and  filter ;  or 
dissolve  1  part  of  molybdate  of  ammonium  in  3  or  4  parts  of  weak 
ammonia-water,  and  mix  the  liquid  with  12  or  15  parts  of  nitric  acid, 
as  before. 

23.  *  Sodium  Hydrate.  —  Place  1  part,  by  weight,  of  the  best 
commercial  caustic  soda  in  a  large,  stoppered  bottle ;  pour  upon  it  8 
or  9  parts  of  water,  and  shake  the  bottle  at  intervals  until  the  whole 
of  the  soda  has  dissolved.  Leave  the  bottle  at  rest  until  the  liquid 
has  become  clear,  and  finally  transfer  the  solution,  with  a  siphon,  to 
the  small  bottles  in  which  it  is  to  be  kept  for  use.    The  solution  thus 


§§  24, 25.]  REAGENTS.  153 

prepared,  though  pure  enough  for  the  uses  prescribed  in  this  manual, 
is  really  far  from  pure.  It  would  be  unfit  for  use  in  a  delicate  research, 
because  it  is  usually  contaminated  with  chloride,  sulphate  and  carbo- 
nate of  sodium,  and  is  liable  to  contain  traces  of  aluminate,  phosphate 
and  silicate  of  sodium.  Since  some  nitrate  of  sodium  is  added  to  it 
in  the  process  of  manufacture,  the  soda  is  liable  to  be  contaminated 
with  this  salt  and  the  products  of  its  decomposition,  including  ammonia. 
This  last  impurity  is  liable  to  be  given  off  when  the  solution  is  boiled. 

Potassium  hydrate  (caustic  potash)  may  be  substituted  for  caustic 
soda  whenever  it  can  be  more  readily  obtained.  The  potash  should 
be  dissolved  in  about  10  parts  of  water. 

Since  solutions  of  the  caustic  alkalies  act  upon  glass  rather  easily, 
especially  when  its  outer  surface  or  "fire-glaze"  has  once  been 
removed,  it  often  happens,  when  the  soda  solution  is  kept  in  glass- 
stoppered  bottles,  that  the  stoppers  become  immovably  cemented  to 
the  glass  by  the  silicate  of  sodium  which  forms  in  their  necks.  This 
difficulty  may  be  avoided  by  wiping  the  necks  of  the  bottles  dry  after 
any  of  the  solution  has  been  poured  from  them  ;  but  it  will  usually  be 
found  more  convenient  to  replace  the  glass  stoppers  with  plugs  of 
vulcanized  caoutchouc,  or  better  still,  with  small  glass  stoppers,  over 
the  bodies  of  which  short  pieces  of  caoutchouc  tubing  have  been 
stretched.  Solutions  of  the  caustic  alkalies  should  be  kept  in  bottles 
made  of  glass  which  is  free  from  lead. 

24.  *  Sulphide  of  Sodium.  —  Dissolve  1  part,  by  weight,  of  com- 
mercial sulphide  of  sodium,  if  it  can  be  obtained,  in  8  parts  of  water. 
Sulphide  of  sodium  may  be  made  by  melting  together  in  an  iron  pot 
or  ladle  a  mixture  of  dry  carbonate  of  sodium  with  an  equal  weight  of 
sulphur.  This  operation  does  not  require  a  great  deal  of  heat,  and  it 
may  be  performed  over  the  blast  lamp  or  over  an  ordinary  coal  fire. 
Sulphide  of  potassium  is  not  an  available  substitute  for  sulphide  of 
sodium. 

25.  *  Carbonate  of  Sodium.  —  For  most  purposes  it  is  essential 
that  the  sodium  carbonate  should  be  free  from  sodium  sulphate. 
Pure  dry  carbonate  may  be  obtained  from  the  dealers  in  chemicals, 
or  it  may  be  prepared  by  washing  a  pound  or  two  of  bicarbonate  of 
sodium  repeatedly,  upon  a  filter,  with  small  quantities  of  ice-cold 
water,  until  the  original  quantity  is  reduced  to  a  fifth  or  a  sixth  of  its 
bulk.  The  powder  is  then  dried,  ignited,  and  kept  in  well-stoppered 
bottles.  For  the  solution,  dissolve  1  part  of  the  salt  in  4  parts  of 
water. 


154  BE  AGENTS,  C§§  26^6- 

26.  Biborate  of  Sodium  (Borax).  —  Common  borax,  powdered. 

27.  Phosphate  of  Sodium.  —  Dissolve  1  part,  by  weight,  of 
"  common  phosphate  of  soda  "  in  10  parts  of  water. 

28.  Acetate  of  Sodium.  —  Dissolve  1  part  of  the  crystallized  salt 
in  10  parts  of  water. 

29.  Nitrate  of  Sodium.  —  Select  a  clean,  white  sample  of  the 
commercial  salt,  and  keep  in  the  form  of  a  coarse  powder. 

30.  Acid  Sulphate  of  Sodium.  —  Heat  a  mixture  of  16  parts, 
by  weight,  of  Glauber's  salt,  and  5  parts  of  concentrated  sulphuric 
acid,  in  a  platinum  vessel,  until  a  portion  of  the  melted  mass  becomes 
distinctly  solid  when  taken  up  on  a  glass  rod.  Then  allow  the  mix- 
ture to  become  cold  ;  remove  the  cold  lump  from  the  platinum  vessel, 
and  break  it  into  fragments.  Keep  the  coarse  powder  in  a  tight,  glass- 
stoppered  bottle.    The  commercial  salt  will  answer. 

31.  Sulphate  of  Potassium.  —  Dissolve  1  part,  by  weight,  of  the 
crystallized  salt,  in  200  parts  of  water.  A  solution  of  this  strength 
contains  the  same  proportional  quantity  of  sulphuric  acid  as  is  con- 
tained in  a  saturated  aqueous  solution  of  sulphate  of  calcium.  Hence 
it  cannot  precipitate  the  latter  when  added  to  solutions  of  the  soluble 
calcium  salts. 

32.  Chromate  of  Potassium.  —  (The  normal  or  "neutral"  yel- 
low chromate.)  Dissolve  1  part,  by  weight,  of  the  salt  in  8  parts  of 
water. 

33.  Bichromate  of  Potassium.  —  The  pure  crystallized  salt  is 
kept  in  the  form  of  powder.     It  must  be  entirely  free  from  chloride. 

34.  Ferrocyanide  of  Potassium. — (  Yellow  Prussiate  of  Potash.) 
Dissolve  1  part,  by  weight,  of  the  commercial  salt  in  12  parts  of 
water. 

35.  Ferricyanide  of  Potassium.  —  (Red  Prussiate  of  Potash.) 
Since  the  aqueous  solution  of  this  salt  undergoes  decomposition,  with 
formation  of  some  ferrocyanide,  when  kept  for  any  length  of  time, 
the  salt  should  be  kept  for  use  in  the  form  of  powder.  The  com- 
mercial salt  is  pure  enough  for  analytical  purposes.  A  minute  frag- 
ment of  it  may  be  dissolved  in  water  at  the  moment  of  use. 

36.  Cyanide  of  Potassium. — The  better  sorts  of  the  commer- 
cial article  are  pure  enough  for  analytical  purposes.  It  should  be 
kept  in  the  solid  form  in  a  tightly  stoppered  bottle.  When  the  solu- 
tion is  required,  dissolve  1  part  of  the  salt  in  4  parts  of  cold  water. 


§§  37-43]  BE  AGENTS.  155 

37.  Nitrate  of  Potassium.  —  Refined  saltpetre  may  be  employed. 
It  should  be  kept  in  the  state  of  powder. 

38.  Nitrite  of  Potassium.  —  Weigh  out  8  parts  of  concentrated 
nitric  acid,  mix  it  with  an  equal  weight  of  water,  and  place  the  mix- 
ture in  a  glass  flask  provided  with  a  perforated  cork  and  gas  delivery- 
tube.  The  flask  should  be  so  large  that  the  mixture  only  half  fills  it. 
Throw  into  the  liquid  2  parts  of  starch,  in  lumps,  and  heat  the  mix- 
ture imtil  red  fumes  of  nitrous  and  hyponitric  acids  begin  to  be  given 
off ;  then  remove  the  lamp  lest  the  action  become  too  violent.  Conduct 
the  fumes  into  a  bottle  containing  5  parts  of  potash-lye  of  1.27  sp. 
gr.,  until  the  latter  is  saturated.  Then  filter  the  saturated  liquid,  and 
evaporate  it  to  dryness.  For  use,  dissolve  1  part  of  the  dry  salt  in  2 
parts  of  water. 

The  nitrite  of  potassium  bought  of  dealers  in  fine  chemicals  is 
often  unfit  for  the  uses  prescribed  in  this  manual ;  it  can  readily  be 
made  good,  however,  by  dissolving  it  in  twice  its  weight  of  water  and 
saturating  the  solution  with  nitrous  fumes. 

39.  Iodide  of  Potassium  and  Starch  Papers.  —  Dissolve  a 
gramme  of  pure  iodide  of  potassium  (free  from  iodate)  in  200  cubic 
centimetres  of  water.  Heat  the  solution  moderately  in  a  porcelain 
dish,  and  stir  into  it  10  grms.  of  starch  which  has  been  reduced  to 
the  consistence  of  cream  by  rubbing  it  in  a  mortar  with  a  small 
quantity  of  water.  Stir  the  mixture  until  it  gelatinizes,  taking  care 
not  to  bum  the  starch,  then  allow  the  paste  to  cool,  and  spread  it 
thinly  upon  one  side  of  white  glazed  paper  with  a  wooden  spatula. 
Dry  the  paper,  cut  it  into  strips  as  large  as  the  little  finger  and  pre- 
serve it  in  stoppered  bottles  kept  carefully  closed. 

40.  Nitrate  of  Silver.  —  Dissolve  1  part,  by  weight,  of  the  com- 
mercial crystals  in  20  parts  of  water. 

41.  Slaked  Lime.  —  Mix  common  quicklime  with  half  its  weight 
of  water.    Keep  the  powder  in  bottles  with  tight  stoppers. 

42.  *  Lime- Water.  —  Place  a  handful  of  slaked  lime  in  a  large 
bottle,  pour  in  enough  water  to  almost  fill  the  bottle,  cork  the  latter 
tightly,  and  shake  it  at  intervals  during  several  days.  Decant  the 
clear  liquid  into  smaller  bottles  for  use.  Refill  the  large  supply-bottle 
with  water,  and  again  shake  it  at  intervals. 

43.  Chloride  of  Calciimi.  —  Stir  powdered  white  marble  into 
dilute  hydrochloric  acid  until  the  acid  is  saturated,  and  dilute  1  part 
of  the  concentrated  solution  with  5  parts  of  water. 


156  KEAGENTS.  [§§44-53. 

44.  *  Chloride  of  Barium.  —  Dissolve  1  part,  by  weight,  of  the 
commercial  salt  in  10  parts  of  water. 

45.  Nitrate  of  Barium.  —  Dissolve  1  part,  by  weight,  of  the 
commercial  salt  in  15  parts  of  water, 

46.  *  Acetate  of  Lead.  —  Dissolve  1  part,  by  weight,  of  "  sugar 
of  lead  "  in  10  parts  of  water,  and  filter. 

47.  Lead  Paper.  —  Slightly  moisten  filter  paper  with  a  solution 
of  acetate  of  lead  at  the  moment  of  use. 

48.  Chloride  of  Magnesium  and  Chloride  of  Ammonium 
(Magnesium  Solution) .  —  Dissolve,  without  heating,  65  grms.  of 
crystallized  chloride  of  magnesium  and  165  grms.  of  commercial  chloride 
of  ammonium  in  water ;  add  260  cubic  centimetres  of  ammonia-water, 
and  dilute  the  liquor  to  the  volume  of  a  litre.  If  less  than  a  litre  of  the 
reagent  is  required,  the  weights  above  given  may,  of  course,  be  reduced 
in  any  desired  proportion.  Let  the  solution  stand  two  or  three  days, 
and  filter  it,  to  separate  any  precipitate  of  ferric  hydrate  or  other 
insoluble  matters,  which  may  have  been  present  as  impurities  in  the 
components  of  the  mixture.     Preserve  the  clear  liquid. 

From  a  solution  thus  prepared  no  hydrate  of  magnesium  can  be 
precipitated  by  ammonia-water ;  herein  consists  the  advantage  of  the 
mixture  as  a  test  for  phosphoric  and  arsenic  acids, 

49.  Ferric  Chloride.  —  Dissolve  1  part,  by  weight,  of  the  salt  in 
15  parts  of  water ;  or  this  solution  can  be  prepared  by  passing  chlorine 
gas  through  a  saturated  solution  of  iron  tacks  in  hydrochloric  acid, 
until  a  drop  of  the  fluid  no  longer  produces  a  blue  precipitate  in  a 
solution  of  ferricyanide  of  potassium.  The  solution  is  then  heated,  to 
expel  the  excess  of  chlorine. 

50.  Nitrate  of  Cobalt.  —  Dissolve  1  part,  by  weight,  of  the  crys- 
tallized salt  in  10  parts  of  water. 

51.  Sulphate  of  Copper.  —  Dissolve  1  part,  by  weight,  of  the 
crystallized  salt  (blue  vitriol)  in  10  parts  of  water. 

52.  Stannous  Chloride.  —  This  solution  is  prepared  by  boiling 
scraps  of  tin  with  strong  hydrochloric  acid  until  hydrogen  ceases  to  be 
evolved.  The  tin  must  be  in  excess.  The  solution  is  diluted  with 
4  times  its  bulk  of  water  acidulated  with  hydrochloric  acid,  and 
filtered,  if  necessary.  The  clear  liquid  must  be  kept  in  a  tightly  closed 
bottle  containing  some  bits  of  tin. 

53.  Black  Oxide  of  Manganese.  —  The  artificially  prepared 
pure  binoxide  of  manganese. 


§§  54-59.]  REAGENTS.  157 

54.  Red  Ozide  of  Mercury.  —  The  commercial  oxide.  It  should 
leave  no  residue  when  heated  upon  platinum  foil. 

55.  Chloride  of  Mercury.  —  Dissolve  1  part  of  mercuric  chloride 
("  corrosive  sublimate  ")  in  20  parts  of  water. 

56.  Platinic  Chloride.  —  Dissolve  1  part  of  the  salt  in  10  parts 
of  water.  Also  prepared  by  dissolving  old  platinum  foil  in  aqua  regia 
as  follows :  cut  the  worn-out  platinum  foil  and  scraps  of  wire  into 
very  fine  pieces,  and  boil  them  in  a  porcelain  dish,  with  successive 
small  portions  of  aqua  regia,  until  all  the  metal  has  dissolved.  Col- 
lect the  several  portions  of  aqua  regia  partially  saturated  with  plati- 
num in  another  dish,  and  evaporate  nearly  to  dryness  on  a  water- bath. 
Dissolve  the  residue  in  water,  with  the  addition  of  a  few  drops  of 
hydrochloric  acid,  and  filter.  Add  chloride  of  ammonium  solution  to 
the  clear  liquid ;  collect  the  precipitated  chloroplatinate  of  ammonium 
on  a  filter,  wash  thoroughly,  dry  and  ignite  in  a  porcelain  crucible  or 
small  evaporating-dish.  Redissolve  the  spongy  platinum  obtained  in 
aqua  regia.  Evaporate  to  dryness  on  a  water-bath,  adding  a  little 
hydrochloric  acid.    Dissolve  the  residue  in  10  parts  of  water. 

57.  Zinc.  —  The  commercial  sheet  metal,  although  usually  con- 
taminated with  lead  and  cadmium,  and  often  containing  faint  traces 
of  arsenic  and  sulphur,  will  generally  be  found  pure  enough  for  the 
purposes  of  this  manual. 

58.  "Solution  of  Indigo"   (Sulphindigotic  Acid).— Pour  5 

parts  (5  grms.  will  be  ample)  of  fuming  sulphuric  acid  into  a  beaker, 
place  the  latter  in  a  dish  of  water  to  keep  it  cool,  and  stir  into 
the  acid,  little  by  little,  1  part  of  finely  powdered  indigo.  When  all 
the  indigo  has  been  added  to  the  acid,  leave  the  mixture  at  rest  for 
48  hours ;  then  pour  it  into  20  times  its  own  volume  of  water,  filter 
the  mixture,  and  preserve  the  filtrate  for  use.  Instead  of  6  parts  of 
fuming  sulphuric  acid,  12  or  14  parts  of  the  ordinary  strong  acid  may 
be  employed ;  in  this  case,  however,  the  mixture  must  be  heated  for 
several  hours  on  a  water-bath.  The  commercial  "  Indigo  Paste  "  will 
answer. 

59.  Litmus  Paper.  —  Heat  1  part,  by  weight,  of  commercial  litmus 
with  6  parts  of  water,  upon  a  water- bath  for  several  hours,  taking 
care  to  replace  the  water  which  evaporates.  Filter,  divide  the  filtrate 
into  two  equal  portions,  and  stir  one  half  repeatedly  with  a  glass  rod 
dipped  in  very  dilute  nitric  acid,  until  the  color  appears  distinctly  red. 
Pour  the  blue  and  red  halves  into  a  porcelain  dish,  and  stir  the  mix- 
ture.    Draw  strips  of  fine  unsized  paper  through  the  liquid,  and  hang 


158  REAGENTS,  [§§  60-66. 

them  on  cords  to  dry.  The  color  of  the  paper  thus  obtained  is  not 
blue,  but  bluish- violet.  It  turns  blue  when  touched  with  an  alkali, 
and  red  when  exposed  to  acids,  and  may  be  used  indifferently  as  a 
test  for  either  acids  or  alkalies. 

60.  Starch  Paste  should  be  prepared,  when  wanted  for  use,  by 
boiling  30  cubic  centimeters  of  water  in  a  porcelain  dish,  and  stirring 
into  it  half  a  gramme  of  starch  which  has  previously  been  reduced  to 
the  consistence  of  cream  by  rubbing  it  in  a  mortar  with  a  few  drops 
of  water. 

61.  Alcohol.  —  Common  alcohol  of  85  or  90  per  cent. 

62.  Water.  —  Clean  rain-water  will  serve  well  enough  for  most 
of  the  purposes  of  this  manual.  In  granitic  regions  the  water  of  many 
lakes,  brooks  and  ponds  also  is  nearly  pure.  Pure  water  may  be 
obtained  by  melting  blocks  of  compact  ice,  or  by  distilling  ordinary 
water  in  glass  or  copper  retorts  and  rejecting  the  first  portions  of  the 
distillate.  It  should  yield  no  precipitate  when  tested  with  chloride  of 
barium  and  nitrate  of  silver. 

63.  Hypochlorite  of  Sodium. —  The  "chloride  of  soda"  of  the 
druggists.  Prepare  by  shaking  up  1  part  of  bleaching  powder  with  10 
parts  of  water ;  add  a  saturated  solution  of  commercial  carbonate  of 
sodium  as  long  as  a  precipitate  is  produced.  Let  the  turbid  mixture 
settle,  and  siphon  off  the  clear  liquid. 

64.  Bisulphide  of  Carbon.  —  Commercial.  Great  care  should  be 
taken  in  using  the  reagent,  as  it  is  extremely  inflammable,  and  the 
vapor  mixed  with  air  is  violently  explosive. 

65.  Chlorine  Water.  —  A  solution  of  chlorine  in  water.  It  should 
be  kept  in  a  well-stoppered  bottle  and  not  exposed  to  light.  Otherwise 
it  is  speedily  converted  into  hydrochloric  acid  with  evolution  of 
oxygen. 


§66.]  KNOWN  SOLUTIONS.  159 


SOLUTIONS  OF  KNOWN  COMPOSITION. 

66.  In  case  the  experiments  indicated  in  Part  I  are  to  be  per- 
formed by  a  considerable  number  of  students,  it  will  be  found  conven- 
ient to  prepare  beforehand  a  moderate  supply  of  the  various  solutions 
required  in  making  the  known  mixtures  under  the  several  classes. 
These  solutions  may  be  made  of  the  strengths  indicated  below. 

Chloride  of  Copper.  —  Dissolve  black  oxide  of  copper  in  5  times 
its  weight  of  a  mixture  of  equal  parts  of  strong  hydrochloric  acid  and 
water.  Dilute  the  resulting  solution  with  3  times  its  bulk  of  water. 
[A  single  student,  in  performing  the  experiment,  may  dissolve  a  few 
grains  of  the  oxide  in  a  small  quantity  of  the  strong  acid,  and,  in 
general,  may  make  the  solutions  as  needed  for  use  by  taking  a  crystal 
or  a  small  amount  of  the  required  substance  in  powder,  as  the  case 
may  be,  without  regard  to  the  exact  amount.  It  is  well,  however,  not 
to  start  with  such  quantities  as  to  make  the  precipitates  inconveniently 
bulky.] 

Araenious  Oxide.  —  Dilute  a  quantity  of  hydrochloric  acid  with 
half  its  bulk  of  water,  and  saturate  it  with  arsenious  oxide  at  a  gentle 
heat.  When  the  solution  has  become  cold,  pour  off  the  clear  liquor 
from  the  arsenious  oxide  which  has  crystallized  out. 

Ferrous  Chloride.  —  Treat  warm  dilute  hydrochloric  acid  (App., 
§  3)  with  as  much  iron  (wire  or  filings)  as  it  will  dissolve,  and  then 
dilute  the  solution  with  an  equal  bulk  of  water.  [This  solution  should 
be  prepared  only  in  small  quantity,  and  kept  in  a  well-stoppered 
bottle.] 

Chloride  of  Zinc*.  —  To  a  quantity  of  hydrochloric  acid  diluted 
with  an  equal  bulk  of  water,  add  as  much  zinc  as  the  acid  will  dis- 
solve, and  then  add  to  the  solution  5  times  its  bulk  of  water. 

Chloride  of  Calcium.  —  Stir  powdered  white  marble  or  chalk  into 
hydrochloric  acid  diluted  with  twice  its  bulk  of  water  until  the  acid  is 
saturated  ;  filter  the  solution,  if  necessary. 

Chloride  of  Magnesium.  —  Dissolve  1  part  of  the  salt  in  10  parts 
of  water,  or  add  "  magnesia  alba  "  to  dilute  hydrochloric  acid  until 
the  acid  is  saturated,  then  dilute  the  solution  with  twice  its  bulk  of 
water. 

Chloride  of  Sodium.  —  Dissolve  common  salt  in  10  times  its 
weight  of  water. 


160  KNOWN   SOLUTIONS.  [§66. 

Nitrate  of  Silver.  —  Dissolve  the  crystallized  salt  in  10  times  its 
weight  of  water. 

Mercurous  Nitrate.  —  Dilute  a  small  quantity  of  strong  nitric 
acid  with  an  equal  bulk  of  water,  and  to  the  mixture,  warmed  over 
the  lamp,  add  more  mercury  than  will  dissolve.  When  action  has 
ceased,  dilute  the  solution  with  5  times  its  bulk  of  water  and  keep  in 
a  bottle  containing  a  small  amount  of  metallic  mercury. 

Nitrate  of  Lead.  —  Dissolve  the  crystallized  salt  in  5  times  its 
weight  of  water. 

Mercuric  Chloride.  —  Dissolve  corrosive  sublimate  in  20  times  its 
weight  of  water. 

Chloride  of  Bismuth.  —  Dissolve  metallic  bismuth  in  aqua  regia. 
When  the  acid  is  saturated  pour  off  the  solution  from  the  undissolved 
metal,  dilute  it  with  twice  its  bulk  of  water  and  add  strong  hydro- 
chloric acid  to  dissolve  the  precipitated  oxy- chloride.  Or,  dissolve  the 
commercial  sub-nitrate  in  hydrochloric  acid  and  dilute  as  before. 

Chloride  of  Cadmium.  —  Dissolve  the  commercial  salt  in  10  times 
its  weight  of  water. 

Chloride  of  Lead.  —  Boil  dilute  hydrochloric  acid  with  an  excess 
of  litharge  and  filter  the  solution  when  perfectly  cold. 

Chloride  of  Antimony.  —  Dilute  the  commercial,  strong  solution 
with  an  equal  bulk  of  water,  and  add  strong  hydrochloric  acid  to  dis- 
solve the  basic  chloride  which  is  precipitated.  Or,  dissolve  the  finely 
powdered  metal  in  aqua  regia  and  dilute  as  before. 

Sulphate  of  Manganese.  —  Dissolve  the  crystallized  salt  in  10 
times  its  weight  of  water. 

Common  Alum.  —  Dissolve  in  10  times  its  weight  of  water. 

Chrome  Alum.  —  Dissolve  in  10  times  its  weight  of  water  without 
heating. 

Bone  Ash  (p.  47)  had  better  be  kept  in  powder  and  dissolved  as 
needed,  in  order  that  the  student  may  not  lose  sight  of  the  fact  that 
this  compound  requires  an  acid  solvent. 

Nitrate  of  Cobalt.  —  Dissolve  in  10  times  its  weight  of  water. 

Nitrate  of  Nickel.  —  Dissolve  in  10  times  its  weight  of  water. 
(The  chlorides  of  nickel  and  cobalt  answer  equally  well,  and  the  solu- 
tions may  be  made  of  the  same  strength.) 


^66.]  KNOWN  SOLUTIONS.  161 

Chloride  of  Barium.  —  Dissolve  the  crystallized  salt  in  5  times 
its  weight  of  water. 

Chloride  of  Strontium.  —  Dissolve  the  crystallized  salt  in  5  times 
its  weight  of  water,     (The  nitrate  will  answer  equally  well.) 

Chloride  of  Tin.  —  Use  the  reagent  (App.,  §  52). 

Nitrate  of  Potassium.  —  Dissolve  1  part  of  the  commercial  salt 
in  5  parts  of  water. 

Sulphate  of  Sodiiun.  —  Dissolve  1  part  of  Glauber's  salt  in  10 
parts  of  water. 

Phosphate  of  Sodium.  —  Dissolve  commercial  ''phosphate  of 
soda  "  in  10  parts  of  water,  as  in  App.,  §  27. 

Carbonate  of  Sodium. -— Dissolve  1  part  of  "sal  soda"  in  5 
parts  of  water. 

Oxalate  of  Potassium.  —  Dissolve  1  part  of  the  crystallized  salt 
in  5  parts  of  water. 

Tartrate  of  Potassium. —  Dissolve  tartaric  acid  in  5  times  its 
weight  of  water  and  neutralize  it  exactly  with  carbonate  of  potassium. 

Iodide  of  Potassium.  —  Dissolve  1  part  of  the  crystallized  salt  in 
10  parts  of  water. 


162 


tlTHNSlLS. 


in  67,  68. 


UTENSILS. 

67.  The  Implements  required  by  the  student  of  qualitative 
analysis  are  few  and  simple.  Besides  bottles  for  the  reagents  enu- 
merated in  the  foregoing  list,  and  a  few  small  phials  for  the  preser- 
vation of  samples  of  salts  and  mixtures  to  be  analyzed,  there  will 
be  needed  — 


A  dozen  test-tubes, 
A  wooden  test-tube  rack, 
A  test-tube  brush, 
A  nest  of  small  beakers, 
2  or  3  glass  stirring-rods, 
A  small  thistle-,  or  funnel-tube, 
A  larger  thistle-tube  for  the  gas- 
generator, 

1  stick  of  No.  7  glass  tubing  (see 
App.,  §  86), 

2  or  3  sticks  of  No.  5  glass  tub- 
ing, 

3  small  glass  funnels, 
A  small  glass  flask, 

A  small  platinum  crucible  is  also 

very  desirable, 
A  few  packages  of  cut  filters,  or  a 

quire  of  filter-paper, 


A  wash-bottle, 

2  small  evaporating-dishes, 

A  porcelain  crucible, 

1  triangle  of  iron  wire, 

An  iron  ring-stand, 

A  filter-stand, 

A  lamp, 

A  gas- bottle  for  generating  sul- 
phuretted hydrogen, 

A  common  jeweller's  blowpipe, 

A  pair  of  small  iron  pincers  (jew- 
eller's tweezers), 

A  piece  of  platinum  foil, 

A  bit  of  platinum  wire, 

A  few  corks  or  caoutchouc  stop- 
pers, 

A  piece  of  blue  cobalt  glass  (see 
§43). 


68.  Reagent  Bottles.  —  The  bottles  in  which  reagents  are  kept 
should  be  of  cylindrical  shape,  and  rather  high  than  wide.  They 
should  be  closed  with  glass  stoppers  which  fit  accurately,  but  are  not 
very  finely  ground.  Most  of  the  liquid  reagents  may  be  conveniently 
kept  in  narrow-mouthed  bottles  of  the  capacity  of  6  fluid  ounces ;  but 
to  avoid  the  necessity  of  frequently  refilling  the  bottles,  it  is  well  to 
keep  the  solutions  most  commonly  employed  —  namely,  dilute  hydro- 
chloric and  nitric  acids,  ammonia-water,  chloride  of  ammonium  and 
carbonate  of  ammonium  —  in  8- ounce  bottles.  Care  must  be  taken  in 
this  case  to  choose  bottles  of  such  shape  that  they  can  be  readily 
grasped  between  the  thumb  and  fingers. 

For  the  reagents  which  are  to  be  kept  in  the  dry  state,  wide- 
mouthed  bottles  of  the  capacity  of  2  or  3  ounces  should  be  chosen. 


§69.]  BEAGENT    BOTTLES.  163 

Reagent  bottles  should  always  be  made  "  extra-heavy,"  since,  from 
constant  use,  they  are  exposed  to  many  blows.  The  lustrous  "flint- 
glass"  bottles  of  American  or  English  make  are  ill  suited  for  the 
preservation  of  liquid  reagents ;  for  such  glass  is  easily  attacked  by 
many  chemical  agents,  and  is  therefore  likely  to  render  the  reagents 
impure.  The  lettered  reagent  bottles  recently  introduced  and  manu- 
factured by  Whitehall,  Tatum  &  Co.,  Philadelphia,  are  excellent  in 
every  respect. 

Each  reagent  bottle  should  be  kept  in  a  particular  place  on  shelves 
before  the  operator  and  convenient  to  his  hand.  Whenever  a  reagent 
is  to  be  used,  the  bottle  which  contains  it  should  be  grasped  in  the 
right  hand ;  the  stopper  should  be  taken  out  by  pinching  it  between 
the  first  and  second  or  third  and  fourth  fingers  of  the  left  hand,  or  by 
pressing  it  between  the  little  finger  and  palm  of  that  hand.  In  either 
case,  the  bottle  is  withdrawn  from  the  stopper,  and  not  the  stopper 
from  the  bottle.  Neither  bottle  nor  stopper  should  be  put  upon  the 
table  ;  the  stopper  should  be  held  in  the  left  hand  as  long  as  the  bottle 
is  open.  When  the  reagent  has  been  poured  out,  the  bottle  is  imme- 
diately closed,  and  returned  to  its  place  upon  the  shelf.  If  these 
apparently  trifling  particulars  are  scrupulously  attended  to,  no  stopper 
can  ever  be  misplaced,  or  soiled  by  contact  with  liquids  or  dirt  on  the 
table ;  and  the  bottle  will  always  be  found  in  its  proper  place  when 
Instinctively  reached  for.  Moreover,  the  label  on  the  bottle  cannot  be 
injured  by  drops  of  the  reagent,  since  the  liquid  must  necessarily  be 
poured  from  the  back,  or  blank  side  of  the  bottle. 

When  a  stopper  sticks  tightly  in  the  neck  of  a  bottle,  it  may  some- 
times be  loosened  by  pressing  it  first  upon  one  side,  and  then  upon  the 
other,  with  the  thumb  of  the  right  hand,  while  the  fingers  of  that  hand 
grip  the  bottle,  and  the  bottle  is  held  still  with  the  left  hand.  Or  the 
neck  of  the  bottle  may  be  immersed  in  hot  water  for  a  minute  or  two, 
to  expand  the  glass  outside  the  stopper.  The  stopper  can  then  usu- 
ally be  taken  out  without  trouble.  The  hot  water  may  be  conveniently 
applied  by  pouring  a  slow  stream  of  it  from  a  wash-bottle  upon  the 
neck  of  the  bottle.  Another  way  is  to  heat  the  neck  of  the  bottle 
over  a  very  small  flame  of  the  gas-  or  alcohol-lamp.  No  matter  how 
the  glass  is  heated,  the  bottle  must  be  constantly  turned  round  and 
round,  in  order  that  each  side  of  the  neck  may  be  equally  exposed  to 
the  heat  and  the  risk  of  cracking  the  bottle  so  be  lessened. 

69.  Test-tubes  are  little  cylinders  of  thin  glass  with  round,  thin 
bottoms  and  lips  slightly  flared.  Their  length  may  be  from  5  to  7 
inches,  and  their  diameter  from  one  half  to  three  fourths  of  an  inch  ; 


164 


TEST-TUBE  RACK. 


[§§  70,  71. 


they  should  never  be  so  wide  that  the  open  end  cannot  be  closed  by 
the  ball  of  the  thumb. 

Test-tubes  are  used  for  heating  small  quantities  of  liquid  over  the 
gas-  or  spirit-lamp  ;  they  may  generally  be  held  by  the  upper  end  in 
the  fingers  without  inconvenience ;  but  in  case  they  become  too  hot 
to  be  held  in  this  way,  a  strip  of  thick,  folded  paper  may  be  nipped 
round  the  tube,  and  grasped  between  the  thumb  and  forefinger  just 
outside  the  tube. 

Two  precautions  are  invariably  to  be  observed  in  heating  test- 
tubes  :  —  1st.  The  outside  of  the  tube  must  be  wiped  perfectly  dry  ; 
and  2d.  The  tube  must  be  moved  in  and  out  of  the  flame  for  a  minute 
or  two  when  first  heated.  It  should  be  rolled  to  and  fro  also  to  a 
slight  extent  between  the  thumb  and  forefinger,  in  order  that  each  side 
of  it  may  be  equally  exposed  to  the  flame.  A  drop  of  water  on  the 
outside  of  the  tube  keeps  one  spot  cooler  than  the  rest.  The  tube 
breaks,  because  its  parts,  being  unequally  heated,  expand  unequally, 
and  tear  apart. 

When  a  liquid  is  boiling  actively  in  a  test-tube,  it  sometimes  hap- 
pens that  portions  of  the  hot  liquid  are  projected  out  of  the  tube  with 
some  force ;  the  tube  should  therefore  always  be  held  in  an  inclined 
position,  and  the  operator  should  be  careful  not  to  direct  it  towards 
himself,  or  towards  any  other  person  in  his  neighborhood. 

Test-tubes  are  cleaned  by  the  aid  of  cylindrical  brushes  made  of 
bristles  caught  between  twisted  wires,  like  those  used  for  cleaning 
lamp-chimneys  ;  the  brushes  should  have  a  round  end  of  bristles. 

70.  Test-Tube  Rack.  —  Test-tubes  are  kept  in  a  wooden  rack, 
such  as  is  represented  in  Fig.  1.    When  in  use,  the  tubes  stand 

upright  in  the  holes  of  the  rack;  but 
clean  tubes  are  inverted  upon  the  pegs 
behind  the  holes,  in  order  that  they  may 
be  kept  free  from  dust,  and  that  the  last 
portions  of  wash-water  may  drain  away 
from  them  after  washing.  The  rack  should 
be  large  enough  to  hold  a  dozen  tubes. 
Care  should  be  taken  that  the  tubes  are 
washed  perfectly  clean  before  being  in- 
verted on  the  pegs,  lest  the  pegs  themselves  become  dirty. 

71.  Flasks.  —  Small  flasks  of  2  or  3  ounces'  capacity  are  well 
suited  for  the  purposes  of  qualitative  analysis.  When  a  liquid  is  to 
be  boiled  in  a  flask,  the  flask  should  be  placed  upon  a  support  of 


Pigr.  1. 


§§  72-74.]  FILTERING.  165 

wire-gauze  (App.,  §  80),  and  sufficiently  inclined  to  prevent  any  par- 
ticles of  the  liquid  from  being  thrown  out  of  the  neck  by  the  move- 
ment of  ebullition. 

As  with  test-tubes  and  all  other  glass  or  porcelain  vessels  of  what- 
ever form,  the  outside  of  a  flask  nmst  be  wiped  perfectly  dry  before 
exposing  it  to  the  lamp.  The  flame  should  be  moved  about  also 
beneath  the  flask,  at  first,  in  order  that  the  temperature  of  the  latter 
may  be  raised  equally  and  not  too  rapidly. 

72.  Beakers  are  thin,  flat-bottomed  tumblers  with  a  slightly 
flaring  rim.  They  are  bought  in  sets  or  nests.  A  nest  in  which 
the  largest-sized  beaker  has  a  capacity  of  about  6  ounces  will  be  suffi- 
cient for  the  requirements  of  this  work. 

73.  Glass  Funnels  should  be  thin  and  light,  and  should  be  about 
2  or  2.5  inches  in  diameter.  Their  sides  should  incline  at  an  angle 
of  60°.    The  wider  the  throat  of  the  funnel,  the  better. 

74.  Filtering.  —  Paper  filters  are  employed  in  qualitative  analysis 
to  separate  precipitates  from  the  Uquids  in  which  they  have  been 
formed.  A  good  filtering-paper  must  be  porous  enough  to  filter  rap- 
idly, and  yet  sufficiently  close  in  texture  to  retain  the  finest  powders  ; 
and  it  must  also  be  strong  enough  to  bear,  when  wet,  the  pressure  of 
the  liquid  which  is  poured  in  upon  it.  Filter-paper  should  never  con- 
tain any  gypsum  or  other  soluble  material,  and  should  leave  only  a 
small  proportion  of  ash  when  burned.  White  or  light-gray  paper  is  to 
be  preferred  to  colored,  since  it  more  commonly  fulfils  these  require- 
ments. 

Filtering-paper  is  commonly  sold  in  sheets,  which  may  be  cut  into 
circles  of  any  desired  diameters  for  use,  according  to  the  various 
scales  of  operation,  and  quantities  of  liquids  to  be  filtered.  Or  pack- 
ages of  "cut-filters"  may  be  procured  ready-made  from  the  dealers 
in  chemical  wares. 

As  a  general  rule,  small  filters  should  be  employed  in  analytical 
operations ;  the  mixture  to  be  filtered  should  be  poured  by  small  suc- 
cessive portions  upon  a  filter  no  larger  than  is  needed  to  hold  the 
whole  of  the  solid  matter  which  is  to  be  collected.  Filters  about  3 
inches  in  diameter  are  well  suited  for  most  of  the  analytical  operations 
described  in  this  work,  though  there  are  many  cases  where  smaller 
filters  are  required,  and  a  few  instances  in  which  filters  as  large  as 
4  inches  in  diameter  might  be  necessary. 

There  are  two  ready  methods  of  preparing  filters  for  use.    According 


166  FILTERING.  [§  75. 

to  the  first  method,  shown  in  Fig.  2,  a  circle  of  paper  is  folded  over 
on  its  own  diameter,  and  the  semicircle  thus  obtained  is  folded  once 
upon  itself  into  the  form  of  a  quadrant ;  the  paper 
Fiff-  2.  thus  folded  is  opened  so  that  three  thicknesses  shall 

come  upon  one  side,  and  one  thickness  upon  the 
other,  as  shown  in  the  upper  half  of  Fig.  2  ;  the 
filter  is  then  placed  in  a  glass  funnel,  the  angle 
of  which  should  be  precisely  that  of  the  opened 
paper,  viz.  60°.     The  paper  may  be  so  folded  as 
to  fit  a  funnel  whose  angle  is  more  or  less  than 
60°,  but  this  is  the  most  advantageous  angle,  and 
funnels  should  be  selected  with  reference  to  their 
correctness  in  this  respect. 
In  the  second  method  of  folding  filters,  the  circle  of  paper  is  doubled 
once  upon  itself  as  before  into  the  form  of  a  semicircle,  and  a  fold 
equal  to  one  quarter  of  this  semicircle  is  turned  down  on  each  side  of 
the  paper.    Each  of  the  quarter  semicircles  is  then  folded  back  upon 
itself,  as  shown  in  the  lower  half  of  Fig.  3  ;  the  filter  is  opened,  with- 
out disturbing  the  folded  portions,  and  placed  in  the  funnel.     Filtra- 
tion can  be  rapidly  effected  with  this  kind  of  filters,  for  the  projecting 
folds  keep  open  passages  between  the  filter  and  the 
^*     *  funnel,  and  thus  facilitate  the  passage  of  the  liquid. 

That  portion  of  the  circle  of  paper,  which  must 
necessarily  be  folded  up  in  order  to  give  the  requi- 
site conical  form  to  a  paper  filter  retards  filtration 
in  the  first  manner  of  folding,  but  helps  it  in  the 
second. 

A  filter  should  always  be  moistened  with  water 
after  it  has  been  placed  in  the  funnel,  in  order 
that  the  fibres  of  the  paper  may  be  swollen  and 
the  size  of  its  pores  diminished,  before  any  of  the  matter  to  be  filtered 
can  pass  into  them. 

Coarse  and  rapid  filtration  —  as  in  the  preparation  of  reagents  — 
can  be  effected  with  paper  filters  of  large  size,  or  with  cloth  bags ; 
also  by  plugging  the  neck  of  a  funnel  or  leg  of  a  siphon  loosely  with 
tow  or  cotton.  If  a  very  acid  or  very  caustic  liquid,  which  would  de- 
stroy paper,  cotton,  tow,  or  wool,  is  to  be  filtered,  the  best  substances 
wherewith  to  plug  the  neck  of  the  funnel  are  asbestos,  gun-cotton  and 
glass-wool,  neither  of  which  is  attacked  by  such  corrosive  liquids. 

75.  Filter-Stand.  —  Filters  less  than  2  inches  in  diameter  may 
be  placed  directly  in  the  mouth  of  a  test-tube  without  need  of  even  a 


§760 


FILTRATION. 


167 


Fig.  4. 


funnel  to  support  them  ;  and  in  general  the  funnel  which  holds  a  filter 
may  be  thrust  directly  into  the  mouth  of  a  test-tube  whenever  the 
quantity  of  liquid  to  be  filtered  is  small,  if  only  an  ample 
exit  be  provided  for  the  air  in  the  tube,  in  the  manner 
shown  with  the  bottle  of  Fig.  4, 

But  when  the  quantity  of  liquid  to  be  filtered  is  compar- 
atively large,  or  the  operations  to  which  the  filtrate  is  to 
be  subjected  require  that  it  should  be  collected  in  a  beaker 
or  porcelain  dish,  the  funnel  should  have  an  independent 
support.  The  iron  ring-stand,  described  in  §  80  of  this 
Appendix,  may  be  used  for  this  purpose  in  case  of  need ; 
but  wooden  stands  of  the  form  represented  in  Fig.  5, 
adapted  expressly  for  holding  funnels,  are  very  convenient 

and  not  expensive.    The 


Figr.  5. 


\ 


Figr.  6. 


horizontal 
bar  which  holds  the  funnel  may  be 
fixed  at  any  height  on  the  vertical 
square  rod  by  means  of  a  wedge- 
shaped  key,  whose  form  is  shown 
in  the  figure,  or  by  a  wooden  screw. 
A  fine-grained  wood,  which  does  not 
swell  or  shrink  much,  is  desirable  for 
filter-stands. 

In  general,  care  should  be  taken 
that  the  lower  end  of  the  funnel 
touch  the  side  or  edge  of  the  vessel 
into  which  the  filtrate  de- 
scends, in  order  that  the 
liquid  may  not  fall  in 
drops,  but  run  quietly 
without  splashing. 
76.  Rapid  Filtration.  —  Since  in  the  course  of  an 
analysis  much  time  is  consumed  in  the  process  of  filtra- 
tion, it  is  desirable  that  this  operation  should  be  made  as 
rapid  as  possible.  A  considerable  advantage  over  the  ordi- 
nary method  may  be  gained  by  increasing  the  length  of 
the  tube  of  the  funnel  by  the  addition  of  a  piece  of  glass 
tubing  a  metre  or  so  in  length  and  bent  as  represented 
in  Fig.  6.  When  the  funnel  and  the  tube  are  filled  with 
liquid,  the  difference  of  pressure  on  the  upper  and  lower 
surfaces  is  great  enough  to  cause  a  very  sensible  increase  in  the  rapid- 
ity of  the  filtration.    A  far  more  efficient  method  of  hastening  the 


168 


FILTBATION. 


[§76. 


process  of  filtration  by  causing  a  difference  in  pressure  on  the  upper 
and  lower  surfaces  of  the  liquid  to  be  filtered,  may  be  made  available 
wherever  a  constant  supply  of  water  with  a  fall  of  8  or  10  feet  can 
be  obtained.  The  details  of  the  process  and  of  a  convenient  form 
of  the  apparatus  which  may  be  employed,  will  be  described  presently  ; 
the  principle  of  the  method  is  as  follows :  — 

The  filtrate,  instead  of  being  received  in  a  beaker  as  is  usual,  is 
received  in  a  flask  from  which  the  air  is  more  or  less  completely 
exhausted.  This  exhaustion  is  accomplished  by  the  use  of  a  sort 
of  "water-pump"  which  is  an  adaptation  of  a  very  simple  prin- 


Fig.  7. 


ciple.  Let  ab  and  cd  be  two  tubes,  arranged  as 
represented  in  Fig.  7.  If  water  be  allowed  to  flow  in  a 
constant  stream  down  the  tube  ab  and  the  amount  of 
water  supplied  be  properly  regulated,  that  part  of  the 
tube  ab  which  is  below  the  junction  with  cd  will  be 
filled  with  bubbles  of  air,  which  is  drawn  in  continuously 
through  cd  and  dragged  down  by  the  falling  water;  if 
the  tube  at  c  be  connected  with  a  closed  vessel,  the  air 
in  the  vessel  will  be  gradually  exhausted.  The  efficiency  of  such  a 
pump  depends  in  a  measure  upon  the  relative  size  of  the  tubes  and 
the  amount  of  water  supplied.  Various  forms  of  apparatus  in  which 
advantage  is  taken  of  this  general  principle  might  be  and  have  been 
devised.  As  adapted  for  purposes  of  filtration  the  apparatus  is  known 
as  Bunsen's  "  filter- pump."  On  account  of  the  great  advantage  to  be 
gained  by  its  use,  the  apparatus,  and  the  method  of  conducting  the 
filtration  will  be  given  in  detail. 

A  strong  glass  flask  (for  the  purposes  of  qualitative  analysis,  one 
of  from  2  to  4  ounces'  capacity  will  answer)  is  furnished  with  a  doubly- 
perforated  caoutchouc  stopper:  through  one  of  the  perforations  is 
thrust  the  neck  of  a  glass  funnel  and  through  the  other  a  piece  of 
_.  No.  7  glass  tubing,  bent  at  a  right  angle.    This 

tube  serves  to  connect  the  flask  with  the  apparatus 
designed  to  effect  the  rarefaction  of  the  air  in  the 
flask.  If  a  paper  filter  were  put  in  the  funnel,  in 
the  usual  way,  and  filled  with  liquid,  and  any  con- 
siderable difference  of  pressure  were  to  be  brought 
about  between  the  upper  and  lower  surfaces  of  the 
liquid  in  the  filter,  the  paper  would  be  apt  to  break 
and  let  the  precipitate  fall  into  the  flask.  This 
danger  may  be  avoided  by  choosing  a  smooth  glass  funnel  which  has 
an  angle  as  near  60°  as  possible,  and  fitting  into  it  a  second  funnel,  or, 


§76.] 


FILTRATION. 


169 


rather,  a  cone  of  thin  platinum  foil,  the  sides  of  which  possess  exactly 
the  same  inclination  as  those  of  the  glass  funnel.  This  platinum  cone 
is  made  by  cutting  out  from  a  piece  of  the  thinnest  platinum  foil  that 
can  be  obtained,  a  portion  of  a  circle  as  represented  in  Fig.  9,  a.  For 
use  with  a  funnel  2  inches  in  diameter,  this  circle  may  conveniently 
have  a  radius  of  1  inch.  The  foil  is  then  laid  upon  a  piece  _ 
of  hard  wood  and  a  number  of  small  holes  are  punched  out 
of  it.  A  ready  implement  for  this  purpose  is  made  by 
grinding  off  squarely  the  point  of  a  common  sewing-needle 
and  fitting  the  needle  to  a  wooden  handle.  When  gently 
tapped  with  a  hammer,  this  punch  forces  out  a  small  round 
bit  of  the  foil  and,  by  subsequently  rubbing  the  foil  on  the 
bottom  of  a  mortar  with  the  pestle,  any  inequalities  of 
surface  are  avoided.  When  the  foil  has  been  annealed  by 
being  heated  to  redness  in  the  lamp  and  allowed  to  cool,  it 
is  bent  up  into  the  shape  of  a  cone  as  represented  in  Fig.  9,  b. 
This  cone  should  have  the  same  angle  of  inclination  as  the 
funnel  in  which  it  is  to  be  used,  and  it  is  desirable  that  the  funnel 
should  be  of  an  angle  of  60°  ;  still,  if  the  funnel  be  regular  in  shape, 
it  can  be  used  although  it  varies  somewhat  from  this  angle.  The  cone 
is  best  fitted  to  the  funnel  by  the  following  manipulation  :  — 

A  solid  cone  of  close-grained  hard  wood,  or  better  of  brass  (Fig. 
10,  a),  which  has  been  turned  to  an  angle  of  60°,  is  laid  upon  the 
platinum  foil  in  such  a  position  that  the  apex  of 
the  cone  comes  at  the  centre  of  the  circle  of  which 
the  foil  forms  a  part ;  the  foil  is  then  folded  up 
and  shaped  with  the  fingers  so  that  it  fits  the  cone 
closely.  This  wooden  or  brass  cone  is  not  essen- 
tial ;  the  platinum  cone  could  be  shaped  in  the 
funnel  with  proper  care ;  it  is,  however,  very  con- 
venient, especially  in  a  laboratory  where  there  are 
a  number  of  students.  In  procuring  such  a  cone, 
it  is  well  to  lay  out  with  a  protractor  on  a  piece  of  thin  sheet  tin  an 
angle  of  60°,  to  cut  this  out,  and  then  to  give  the  pattern  (templet)  to 
the  workman  employed.  The  two  edges  of  the  foil  lap ;  and  if  they 
were  soldered  in  this  position  the  cone  would,  of  course,  have  an 
angle  of  60°.  The  platinum  cone  is  now  inserted  in  the  funnel  to  be 
used,  and  opened  out  a  little  with  the  fingers,  if  necessary,  so  that  it 
fits  the  glass.  The  funnel  should  differ  so  little  from  60°  that  the 
edges  overlap  each  other  only  slightly  more  or  slightly  less  than  when 
the  foil  was  fitted  to  the  wooden  cone.    By  means  of  a  sharp  point 


170  FILTRATION.  [§  76. 

make  two  scratches  on  the  platinum  cone,  to  show  where  the  over- 
lapping edges  come  when  the  foil  is  in  position,  and  then  remove  the 
cone  from  the  funnel.  Hold  the  platinum  by  means  of  a  pair  of 
pincers  in  the  same  position  that  it  occupied  when  in  the  funnel,  which 
is  easily  done  by  observing  the  scratches  made.  Then  heat  the  cone 
(Fig.  9,  6)  at  the  outer  overlapping  edge,  with  a  blowpipe-flame,  put 
on  a  small  amount  of  powdered  borax,  heat  again,  then  put  on  a  bit 
of  pure  gold,  and  heat  until  the  gold  melts  and  solders  the  two  edges 
together.  The  cone  should  be  held,  the  gold  put  on,  and  the  blowpipe- 
flame  directed  in  such  a  manner  that  the  melted  gold  will  run  down 
towards  the  apex  of  the  cone  and  not  in  the  contrary  direction.  After 
dissolving  off  the  adhering  borax  with  warm  water,  the  cone  is  ready 
for  use.  An  ordinary  paper  filter,  folded  according  to  the  first  method 
of  App.,  §  74,  is  introduced  into  this  compound  funnel  in  the  usual 
manner ;  when  carefully  moistened  and  so  adjusted  that  no  air-bubbles 
are  visible  between  it  and  the  glass,  this  filter,  when  filled  with  a 
liquid,  will  support  the  pressure  ev6n  of  an  extra  atmosphere  without 
breaking. 

A  convenient  form  of  the  Bunsen  pump  is  represented  in  Fig.  11. 
The  tubes  (a&,  5c,  hh)  which  are  represented  in  the  figure  may  be 
very  conveniently  made  of  quarter-inch  lead  pipe  (see  also,  p.  172, 
near  bottom) ,  and  the  bulb-like  enlargement  at  d  may  also  be  made 
of  lead  and  soldered  on  to  the  smaller  pipe.  The  water  is  supplied  in 
not  too  large  amount  by  the  cock  a,  and  as  it  passes  along  the  pipe 
ahc  and  into  the  waste  ck,  it  carries  with  it  a  continual  stream  of 
air-bubbles  dragged  through  hd.  This  tube,  hd,  communicates  indi- 
rectly with  the  flask  F,  which  is  not  connected  immediately  with  the 
pump  ;  the  connection  is  interrupted  by  the  bottle  E,  furnished  with 
a  perforated  stopper  through  which  pass  three  glass  tubes.  One  of 
these  tubes  connects  with  the  flask  F;  one  (by  means  of  caoutchouc 
tubing)  with  the  lead  pipe  h  ;  one  with  the  manometer  m.  The  object 
of  this  bottle  E  is  to  prevent  the  flow  of  water  into  the  flask  F,  in 
case,  as  sometimes  happens,  the  operator  in  letting  on  too  rapid  a 
stream  of  water  causes  it  to  rise  in  the  bulb  d  and  flow  over  in  the 
tube  hh.  All  the  connectors  should  be  of  very  thick  caoutchouc 
tubing  tightly  fitted  and  then  varnished  with  a  strong  solution  of 
shellac;  the  stopper  of  the  bottle  E  may  be  treated  in  the  same 
manner. 

The  manometer  bottle  G  is  a,  convenient  but  not  absolutely  essential 
addition.  It  consists  simply  of  a  small  bottle  containing  a  quantity  of 
mercury,  to  the  surface  of  which  the  atmosphere  has  access  through  a 


76.] 


FILTRATION. 


171 


1T2 


PORCELAIN  DISHES. 


[§77. 


small  glass  tube.  The  tube  m  dips  below  the  mercury  and  connects 
with  the  bottle  E.  As  the  air  is  rarefied  in  E  (and  in  the  flask  F), 
the  mercury  rises  in  the  tube  m ;  this  tube  may  be  marked  in  centi- 
metre or  inch  divisions  by  means  of  a  file,  or  it  may  be  provided  with, 
or  attached  to,  a  paper  or  wooden  scale. 

The  amount  of  rarefaction  that  can  be  produced  by  this  means 
depends,  of  course,  upon  the  head  of  water  accessible,  and  this  will  be 
determined  by  the  difference  in  height  between  the  points  b  and  k, 
the  extremity  of  the  waste-pipe.  With  a  fall  of  35  feet  it  is  possible  to 
obtain  nearly  a  perfect  vacuum,  but  a  fall  of  8  or  10  feet  is  sufficient 
for  the  purposes  of  qualitative  analysis. 

In  operating  the  filter-pump,  certain  precautions  should  be  observed. 
Care  should  be  taken  that  the  water  be  not  supplied  in  too  large  an 
amount.  To  this  end  it  is  well  to  have  the  cock  or  valve  so  arranged 
as  to  make  it  impossible  to  let  on  more  water  than 
experience  shows  to  be  necessary.  The  greatest  effect 
is  produced  by  the  smallest  amount  of  water  that  will 
drag  the  air  down  the  pipe  ck  in  the  form  of  bub- 
bles, and  in  order  to  observe  the  flow  of  air  it  is  well 
to  make  a  portion  of  the  pipe  k  of  glass.  (For  that 
matter,  all  the  pipes  may  be  made  of  glass  tubes 
joined  by  thick  caoutchouc  connectors  ;  glass  tubing 
of  size  No.  5  (see  App,,  §  86)  will  answer;  and  the 
bulb  d  may  also  be  blown  of  glass  by  a  person  pos- 
sessing sufficient  skill.)  In  using  the  pump,  the  water 
should  be  let  on  before  the  connection  is  made  with 
the  filtering  flask,  and  the  flask  should  be  removed 
before  the  water  is  shut  off. 

Instead  of  Bunsen's  pump,  a  small  "Eichards's 
Aspirator"  (Fig.  12),  may  be  used  where  the  water 
supply  is  abundant.  This  "  filter-pump  "  is  screwed 
to  a  faucet.  Its  mode  of  action  will  appear  from  the 
diagram  (Fig.  12).  It  can  be  got  from  dealers  in 
chemical  supplies. 

77.  Porcelain  Dishes  and  Crucibles.  —  Small 
open  dishes  which  will  bear  lieat  without  cracking, 
are  much  used  for  boiling  and  evaporating  liquids. 
The  best  evaporating-dishes  are  those  made  of  Berlin 
porcelain,  glazed  both  inside  and  out,  and  provided 
with  a  little  lip  projecting  beyond  the  rim.  The  dishes  made  of 
Meissen  porcelain  are  not  glazed  on  the  outside,  and  are  not  so  durable 


Air 


Foam 


§78.]  LAMPS.  .  173 

as  those  of  Berlin  manufacture  ;  but  they  are  much  cheaper,  and  with 
proper  care  last  a  long  time. 

The  small  Berlin  dishes,  Nos.  "00,"  "0,"  and  "  1,"  are  well  suited 
for  all  the  requirements  of  this  work.  They  will  generally  bear  an 
evaporation  to  dryness  and  subsequent  ignition  over  the  open  flame  of 
a  gas-lamp,  —  as  when  ammonium  salts  are  expelled  from  Class  VII 
(§  43), —  but  it  is  well  to  protect  the  dish  somewhat  by  placing  it 
upon  a  piece  of  wire-gauze,  rather  than  to  support  it  upon  a  simple 
triangle.  The  Meissen  dishes  do  not  so  well  endure  an  open  flame. 
The  cheaper  kinds  of  evaporating-dishes,  made  of  "semi-porcelain," 
should  never  be  subjected  to  this  severe  treatment ;  they  are,  for  that 
matter,  unfit  for  use  in  qualitative  analysis. 

Very  thin,  highly  glazed  porcelain  crucibles,  with  glazed  covers, 
are  made  both  at  Berlin,  and  at  Meissen  near  Dresden.  In  general 
the  Meissen  crucibles  are  thinner  than  the  Berlin,  but  the  Berlin 
crucibles  are  somewhat  less  liable  to  crack ;  both  kinds  are  glazed 
inside  and  out,  except  on  the  outside  of  the  bottom.  The  Berlin  Nos. 
"00"  and  "0,"  respectively  1\  and  1^  inches  in  diameter,  are  best 
suited  for  the  purposes  of  this  manual.  As  the  covers  are  much  less 
liable  to  be  broken  than  the  crucibles,  it  is  advantageous  to  buy  more 
crucibles  than  covers,  whenever  it  is  possible  so  to  do.  Porcelain 
crucibles  are  supported  over  the  lamp  on  an  iron-wire  triangle ;  they 
must  always  be  gradually  heated,  and  never  brought  suddenly  into 
contact  with  any  cold  substance  while  they  are  hot. 

78.   Lamps.  —  The  common  spirit-lamp  will  be  understood  without 
description  from  the  figure  (Fig.  13).    When  not  actually  lighted,  the 
wick  must  be  kept  covered  with  the  glass  cap ;  for  if 
the  wick  were  exposed  to  the  air,  the  alcohol  in  the        ^^^-  ^^• 
spirit  upon  it  would  evaporate  faster  than  the  water, 
and  the  cotton  would  soon  become  water-soaked  and 
incapable  of  being  lighted. 

Whenever  gas  can  be  obtained,  gas-lamps  are  greatly 
to  be  preferred  to  the  best  spirit-lamps.  For  all  ordi- 
nary uses,  the  gas-lamp  known  as  Bunsen's  burner  may 
be  employed.  The  cheapest  and  best  construction  of 
the  lamp  may  be  learned  from  the  following  description 
with  the  accompanying  figure  (Fig.  14).  The  single  casting  of  brass 
ab  comprises  the  tube  h  through  which  the  gas  enters,  and  the  block  a 
from  which  the  gas  escapes  by  two  or  three  fine  vertical  holes  passnig 
through  the  screw  d  and  issuing  from  the  upper  face  of  d,  as  shown  at  e. 
The  length  of  the  tube  6  is  4.5  c.  m.,  and  its  outside  diameter  varies 


174 


BLAST-LAMPS. 


[§79. 


Fig.  14. 


from  0.5  c.  m,  at  the  outer  end  to  1  c.  m.  at  the  junction  with  the  block 
a.  The  outside  diameter  of  the  block  a  is  1.6  c.  m.,  and  its  outside 
height  without  the  screws  is  1.8  c.  m.     By  the  screw  c,  the  piece  ab  is 

attached  to  the  iron  foot  g,  which  may- 
be 6  c.  m.  in  diameter.  By  the  screw  d, 
the  brass  tube  /  is  attached  to  the  cast- 
ing ab.  The  diameter  of  the  face  e, 
and  therefore  the  internal  diameter  of 
the  tube  /,  should  be  8  m.  m.  The 
length  of  the  tube  /  is  9  c.  m.  Through 
the  wall  of  this  tube,  four  holes  5  m.  m. 
in  diameter  are  to  be  cut  at  such  a 
height  that  the  bottom  of  each  hole 
will  come  1  m.  m.  above  the  face  e 
when  the  tube  is  screwed  upon  ab. 
These  holes  are  of  course  opposite  each 
other  in  pairs.  The  finished  lamp  is  also  shown  in  the  figure.  To 
the  tube  b  a  caoutchouc  tube  of  5  to  7  m.  m.  internal  diameter  is 
attached ;  this  flexible  tube  should  be  about  1  m.  long,  and  its  other 
extremity  should  be  connected  with  the  gas- cock  through  the  inter- 
vention of  a  short  piece  of  brass 
gas-pipe  screwed  into  the  cock.  In 
cases  where  a  very  small  flame  is 
required,  as,  for  instance,  in  evapo- 
rating small  quantities  of  liquid,  a 
piece  of  wire-gauze  somewhat  larger 
than  the  opening  of  the  tube  /  should 
be  laid  across  the  top  of  the  tube, 
and  its  projecting  edges  pressed 
down  tightly  against  the  sides  of  the 
tube  before  the  gas  is  lighted.  In 
default  of  this  precaution,  the  flame 
of  a  Bunsen  burner,  when  small  and 
exposed  to  currents  of  air,  is  liable 
to  pass  down  the  tube  and  ignite  the 
gas  at  d. 

79.  Blast-lamps  and  Blowers. 

—  Though  well    suited   for  all   the 

ordinary  operations  of  the  laboratory,  the  lamps  above  described  are 

incapable  of  yielding  a  very  intense  heat.    Hence,  when  the  contents 

of  a  platinum  crucible  are  to  be  fused  or  intensely  heated,  a  blast- 


Fig.  15. 


79.] 


BLOWERS. 


175 


lamp  will  be  found  useful.    The  best  form  is  that  sold  under  the  name 

of  Bunsen's  Gas  Blowpipe.    Its  construction  and  the  method  of  using 

it  may  be  learned  from  the  accompanying  figure  (Fig.  15):  ab  is  the 

pipe  through  which  the  gas  enters ;  c  is 

the  tube  for  the  blast  of  air ;  the  relation  ^^^-  ^^^ 

of  the  air  tube  to  the  external  gas  tube 

is  shown  at  d  ;  there  is  an  outer  sliding 

tube  by  which  the  form  and  volume  of 

the  flame  can  be  regulated. 

If  gas  is  not  to  be  had,  a  lamp  burn- 
ing oil  or  naphtha  may  be  employed.  Fig.  16  represents  a  glass- 
blower's  lamp,  made  of  tin  and  suitable  for  burning  oil.  A  large 
wick  is  essential,  whether  oil  or  naphtha  be  the  combustible. 

For  every  blast-lamp  a  blowing- machine  of  some  sort  is  necessary. 
To  supply  a  constant  blast,  it  is  essential  that  the  bellows  be  of  that 
construction  called  double. 

Figr.  17. 


Fig.  17  represents  a  very  good  form  of  blowpipe-table.     The  bellows 
are  made  of  seamless  rubber  cloth  ^  the  table  is  0,8  meter  high,  from 


17J5 


BLOWERS. 


[§79. 


which  the  other  dimensions  may  be  inferred.  A  simpler  form  of 
bellows,  and  one  which  can  be  made  by  any  carpenter  or  cabinet- 
maker, is  represented  in  perspective  and  in  section  in  Fig.  18.    The 


sides  of  the  bellows  and  of  the  reservoir  are  made  of  stout  leather. 
The  arrangement  of  valves  will  be  evident  from  the  figure  ;  a  constant 
pressure  is  maintained  on  the  reservoir  by  means  of  a  spiral  spring, 
and  the  air  is  delivered  through  the  tube  t.  The  rod  which  is  repre- 
sented in  the  figure  serves  simply  as  a  guide.  The  entire  length  from 
a  to  &  may  be  0.6  meter. 

Where  an  abundant  supply  of  water  is  at  command,  a  Bunsen 
pump  of  the  kind  described  in  App.,  §  76,  but  of  larger  size,  may  be 
used  to  furnish  a  blast.  The  pipe  above  the 
enlargement  d  (see  Fig.  11)  is  left  open  to  the 
air  instead  of  connecting  with  a  flask  as  repre- 
sented in  Fig.  11.  The  waste-pipe  k  passes 
through  the  cork  of  a  large  bottle,  Fig.  19,  of  some 
liters'  capacity.  Through  the  stopper  of  this 
bottle  there  pass  also  two  glass  tubes ;  one  of 
them,  h,  reaches  nearly  to  the  bottom  of  the 
bottle  and  serves  as  a  siphon ;  the  other  merely 
extends  through  the  cork,  and  to  it  is  attached 
the  tube  ?',  to  convey. the  blast  to  any  desired 
point.  The  water  and  air,  which  together  flow 
down  the  pipe  kh,  pass  into  the  bottle.  When 
the  water  is  turned  on,  the  caoutchouc  tube  gi  is 
closed  for  a  moment  with  the  thumb  and  finger. 
This  starts  the  water  through  the  siphon,  and 
immediately  a  continuous  and  po^verful  blast  of 
air  rushes  out  through  the  tube  gi,  and  may  be 
carried  directly  to  the  blowpipe.  The  siphon 
must  be  capable  of  carrying  off  a  larger  stream  of  water  than  that 
which  is  allowed  to  enter,  so  that  there  shall  never  be  more  than 
3  or  4  c.  m.  of  water  in  the  bottle. 


§79.] 


BLOWERS. 


177 


Instead  of  the  Bunsen  Pump,  the  large-sized  Richards' s  Filter-Pump 
may  be  used,  if  there  is  a  sufficient  head  of  water.  The  accompanying 
figure  (Fig.  20)  shows  the  pump  arranged  to  supply  a  blast,  and  the 

Figr.  20. 


WimUWUtK 


L 


dimensions  of  the  blast  attachment  are  given.    The  pump,  with  blast 
attachment,  can  be  obtained  of  dealers  in  laboratory  supplies. 
The  efficiency  of  the  blast  depends  upon  the  dimensions  of  the  tubes 


178 


LAMPS. 


[§80. 


and  the  head  of  water  employed ;  a  fall  of  6  or  8  feet  furnishes  an 
efficient  blast. 

In  default  of  a  blast-lamp,  platinum  crucibles  may  readily  be  ignited 
in  a  fire  of  coke  or  anthracite.  To  this  end,  place  the  tightly  covered 
platinum  crucible  in  a  somewhat  larger  crucible  of  refractory  clay  or 
Hessian  ware,  and  pack  the  space  between  the  two  crucibles  tightly 
with  calcined  magnesia,  so  that  the  platinum  may  nowhere  come  in 
contact  with  the  clay,  ^over  the  coarse  crucible,  and  place  it,  with  its 
contents,  in  the  coal  fire,  in  such  a  manner  that  it  may  be  gradually 
heated  ;  finally,  imbed  the  crucible  in  the  glowing  coals  and  urge  the 
draught  of  the  furnace  for  half  an  hour.  The  degree  of  heat  to  which 
the  contents  of  the  platinum  crucible  may  be  exposed,  in  this  way,  in 
an  efficient  fire,  is  really  far  greater  than  that  of  the  blast-lamps  above 
described  ;  but  the  lamps  are  more  convenient  than  the  fire. 

The  effect  of  a  simple  Bunsen's  burner  may  be  greatly  increased, 
without  the  use  of  any  blower,  by  surrounding  its  flame  with  a 
cylinder  of  fire  clay,  3  inches  in  diameter  by  4  or  5  inches  high,  and 
having  walls  at  least  f  of  an  inch  thick.  The  crucible,  or  other  body 
to  be  heated,  is  hung  in  the  middle  of  this  chimney,  and  is  thus 
exposed  not  only  to  the  direct  heat  of  the  flame,  but  also  to  the  radiant 
heat  from  the  clay  walls  which  surround  it. 

Where  no  gas  is  to  be  had,  an  alcohol-lamp  with  circular  wick, 

of  some  one  of  the  numerous 
^^^-  2^-  forms  sold  under  the  name  of 

Berzelius'  Argand  Spirit-Lamp 
(Fig.  21),  will  be  found  useful. 
These  argand  lamps  are  usually 
mounted  on  a  lamp-stand  pro- 
vided with  three  brass  rings  ; 
but  the  fittings  of  these  lamps 
are  all  made  slender,  in  order 
not  to  carry  off  too  much  heat. 
When  it  is  necessary  to  heat 
heavy  vessels,  other  supports 
must  be  used.  Several  forms 
of  gasoline  burners  are  at  pres- 
ent sold  by  dealers  in  laboratory 
supplies. 

80.  Iron-stand,  Tripod, 
Wire-Gauze  and  Triangle.  —  To  support  vessels  over  the  gas-lamp, 
an  iron-stand  is  used  consisting  of  a  stout  vertical  rod  fastened  into 


81.] 


WATElt-  AND  SAND-BATB. 


179 


Fig.  22. 


k« 


Fig.  23. 


a  heavy  cast-iron  foot,  and  several  iron  rings  of  graduated  sizes 
secured  to  the  vertical  rod  with  binding  screws  ;  all  the  rings  may  "be 
slipped  off  the  rod,  or  any  ring  may  be  adjusted  at  any 
convenient  elevation.  The  general  arrangement  is  not 
unlike  that  of  the  stand  which  makes  part  of  the  Ber- 
zelius  lamp  (Fig.  21),  although  simpler  and  cheaper. 
As  a  general  rule,  it  is  not  best  to  apply  the  direct 
flame  to  glass  and  porcelain  vessels ;  hence  a  piece  of 
iron  wire-gauze  of  medium  fineness  is  stretched  loosely 
over  the  largest  ring,  and  bent  downwards  a  little  for 
the  reception  of  round-bottomed  vessels  ;  on  this  gauze, 
flasks  and  porcelain  dishes  are  usually  supported.  Cru- 
cibles, or  dishes,  too  small  for  the  smallest  ring  belong- 
ing to  the  stand,  are  conveniently  supported  on  an 
equilateral  triangle  made  of  three  pieces  of  soft  iron 
wire  twisted  together  at  the  apices ;  this  triangle  is 
laid  on  one  of  the  rings  of  the  stand.  An  iron  tripod  —  that  is,  a 
stout  ring  supported  on  three  legs  —  may  often  be  used  instead  of  the 
stand  above  described,  but  it  is  not  so  generally 
useful  because  of  the  difliculty  of  adjusting  it  at 
various  heights :  with  a  sufficiency  of  wooden 
blocks  wherewith  to  raise  the  lamp  or  the  tripod 
as  occasion  may  require,  it  may  be  made  avail- 
able. 

81.  Water-Bath  and  Sand-Bath.  —  It  is 
often  necessary  to  evaporate  solutions,  or  to  dry 
precipitates  at  a  moderate  temperature  which 
can  permanently  be  kept  below  a  certain  known  limit ;  thus,  when 
an  aqueous  solution  is  to  be  quietly  evaporated  without  spirting  or 
jumping,  the  temperature  of  the  solution  must 
never  be  suffered  to  rise  above  the  boiling-point  of 
water,  nor  even  quite  to  reach  this  point.  This  quiet 
evaporation  is  best  effected  by  the  use  of  a  water- 
bath, — a  copper  cup  whose  top  is  made  of  concentric 
rings  of  different  diameters  to  adapt  it  to  dishes  of 
various  sizes  (Fig.  24).  This  cup,  two-thirds  full  of 
water,  is  supported  on  the  iron-stand  over  the  lamp, 
and  the  dish  containing  the  solution  to  be  evaporated 
is  placed  on  that  one  of  the  several  rings  which  will  permit  the  greater 
part  of  the  dish  to  sink  into  the  copper  cup.  The  steam  rising  from 
the  water  impinges  upon  the  bottom  of  the  dish,  and  brings  the  liquid 


Fig.  24. 


180 


BLOWPIPES, 


t§82. 


within  it  to  a  temperature  which  insures  the  evaporation  of  the  water, 
but  will  not  cause  any  actual  ebullition.  The  water  in  the  copper  cup 
must  never  be  allowed  to  boil  away.  Wherever  a  constant  supply  of 
steam  is  at  hand,  as  in  buildings  warmed  by  steam,  the  copper  cup 
above  described  may  be  converted  into  a  steam-bath  by  attaching  it 
to  a  steam-pipe  by  means  of  a  small  tube  provided  with  a  stop-cock. 

An  empty  tomato-can  furnished  with  rings  as  above  may  take  the 
place  of  the  copper  cup;  and,  in  fact,  a  cheap  but  serviceable  water- 
bath  may  be  made  from  a  quart  milk-can,  oil-can,  tea-canister,  or  any 
similarly  shaped  tin  vessel,  by  inserting  the  stem  of  a  glass  funnel 
into  the  neck  of  a  can  through  a  well-fitting  cork.  In  this  funnel  the 
dish  containing  the  liquor  to  be  evaporated  rests.  The  can  contains 
the  water,  which  is  to  be  kept  just  boiling.  On  account  of  the  shape 
of  the  funnel,  dishes  of  various  sizes  can  be  used  with  the  same 
apparatus. 

When  a  gradual  and  equable  heat  higher  than  can  be  obtained  upon 
the  water-bath  is  required,  a  sand-bath  will  sometimes  be  found  useful. 
A  cheap  and  convenient  sand-bath  may  be  made  by  beating  a  disk  of 
thin  sheet  iron,  about  4  inches  in  diameter,  into  the  form  of  a 
saucer  or  shallow  pan,  and  placing  within  it  a  small  quantity  of  dry 
sand.  The  disk  or  flask  to  be  heated  is  imbedded  in  the  sand,  and 
the  apparatus  placed  upon  a  ring  of  the  iron-stand  over  a  gas-lamp. 

pj      25  ®2-  Blowpipes.  —  The  mouth-blowpipe   in 

its  simplest  form  is  a  tube  bent  near  one  ex- 
^_/ri        n  tremity  at  a  right  angle.     Fig.  25,  a,  represents 

a  common  form  of  blowpipe  used  by  jewellers. 
The  blowpipe  is  rendered  more  convenient  by 
the  addition  of  a  mouth-piece  and  a  chamber 
near  the  right  angle  for  the  condensation  of 
moisture.  Fig.  25,  b  and  c,  represent  different 
forms  of  blowpipe  thus  furnished.  The  cheap- 
est and  best  form  of  mouth-blowpipe  for  chemi- 
cal purposes  is  a  tube  of  tin-plate,  about  18 
c.  m.  long,  2  c.  m.  broad  at  one  end,  and  tapering 
to  0.7  c.  m.  at  the  other  (Fig.  25,  6);  the  broad 
end  is  closed,  and  serves  to  retain  the  moisture  ; 
a  little  above  this  closed  end  a  small  cylindrical 
tube  of  brass  about  5  c.  m.  long  is  soldered  in  at  right  angles  ;  this 
brass  tube  is  slightly  conical  at  the  end,  and  carries  a  small  nozzle  or 
tip,  which  may  be  made  either  of  brass  or  platinum.  The  tip  should 
be  drilled  out  of  a  solid  piece  of  metal,  and  should  not  be  fastened 


Qw*- 


I 


sss^Bbx 


^ 


82.] 


BL  O  WPIPE-FLAME. 


181 


upon  the  brass  tube  with  a  screw.  A  trumpet-shaped  mouth-piece 
of  horn  or  boxwood  is  a  convenient,  though  by  no  means  essential, 
addition  to  this  blowpipe.  For  convenience  in  cleaning  and  packing, 
blowpipes  are  often  made  in  several  pieces,  as  is  the  one  represented 
in  Fig.  25,  c. 

The  blowpipe  may  be  used  with  a  candle,  with  gas  or  with  any 
hand-lamp  proper  for  burning  oil,  petroleum  or  any  of  the  so-called 
burning  fluids,  provided  that  the  form  of  the  lamp  below  the  wick- 
holder  is  such  as  to  permit  the  close  approach  of  the  object  to  be 
heated  to  the  side  of  the  wick.  When  a  lamp  is  used,  a  wick  about 
1.2  c.  m.  long  and  0.5  c.  m.  broad  is  more  convenient  than  a  round  or 
narrow  wick.  The  wick-holder  should  be  filed  off  on  its  longer  dimen- 
sion a  little  obliquely,  and  the  wick  cut  parallel  to  the  holder,  in  order 
that  the  blowpipe-flame  may  be  directed  downwards  when  necessary 
(Figs.  26  and  27).  A  gas-flame  suitable  for  the  blowpipe  is  readily 
obtained  by  slipping  a  narrow  brass  tube  (i)  open  at  both  ends,  into 
the  tube  /  of  Bunsen's  burner.  (See  Fig.  13.)  This  blowpipe-tube 
must  Ve  long  enough  to  close  the  air-apertures  in  the  tube  /,  and 
should  be  pinched  together  and  filed  off  obliquely  on  top;  it  may 
usually  be  obtained  with  the  burner  from  dealers  in  chemical  ware. 

To  use  the  mouth-blowpipe,  place  the  open  end  of  the  tube  between 
the  lips,  or,  if  the  pipe  is  provided  with  a  mouth-piece,  press  the 
trumpet-shaped  mouth-piece  against  the  lips  ;  fill  the  mouth  with  air 
till  the  cheeks  are  widely  distended,  and  insert  the  tip  in  the  flame  of 
a  lamp  or  candle ;  close  the  communication  between  the  lungs  and 
the  mouth,  and  force  a  current  of  air  through  the  tube  by  squeezing 
the  air  in  the  mouth  with  the  muscles  of  the  cheeks,  breathing,  in  the 
meantime,  regularly  and  quietly  through  the  nostrils.  The  knack  of 
blowing  a  steady  stream  for  several  minutes  at  a  time,  is  readily 
acquired  by  a  little  practice. 

It  will  be  at  once  observed  ^^S".  26. 

that  the  appearance  of  the 
flame  varies  considerably, 
according  to  the  strength  of 
the  blast  and  the  position  of 
the  jet  with  reference  to  the 
wick. 

When  the  jet  of  the  blow- 
pipe is  inserted  into  the  mid- 
dle of  a  candle-flame,  or  is  placed  in  the  lamp-flame  in  the  position 
shown  in  Fig.  26,  and  a  strong  blast  is  forced  through  the  tube,  a  long, 


182  BLOWPIPE-FLAME.  [§  82. 

blue  cone  of  flame,  a  6,  is  produced,  beyond  and  outside  of  which 
stretches  a  more  or  less  colored  outer  cone  towards  c.  The  point  of 
greatest  heat  in  this  flame  is  at  the  point  of  the  inner  blue  cone, 
because  the  combustible  gases  are  there  supplied  with  just  the  quantity 
of  oxygen  necessary  to  consume  them,  but  between  this  point  and  the 
extremity  of  the  flame  the  combustion  is  concentrated  and  intense. 
The  greater  part  of  the  flame  thus  produced  is  oxidizing  in  its  effect, 
and  this  flame  is  technically  called  the  oxidizing -flame.  From  the  point 
a  of  the  inner  blue  cone,  the  heat  of  the  flame  diminishes  in  both  direc- 
tions, towards  6,  on  the  one  hand,  and  towards  c  on  the  other ;  most 
substances  require  the  temperature  which  is  found  between  a  and  c. 
Oxidation  takes  place  most  rapidly  at  or  just  beyond  the  point  c  of 
the  flame,  provided  that  the  temperature  at  this  point  is  high  enough 
for  the  special  substance  to  be  heated. 

A  flame  of  precisely  the  opposite  chemical  effect  may  be  produced 
with  the  blowpipe.    To  obtain  a  good  redwcin^-flame,  it  is  necessary 

to  place  the  tip  of  the  blow- 
Fig.  27.  pipe,  not  within,  but    just 
.^.7r^\                                                       outside   of   the  flame,  and 
"■^                                                to    blow  rather    over   than 

through  the  middle  of  the 
flame  (Fig.  27).  In  this 
manner,  the  flame  is  less 
altered  in  its  general  char- 
acter than  in  the  former 
case,  the  chief  part  con- 
sisting of  a  large,  luminous 
cone,  containing  a  quantity  of  free  carbon  in  a  state  of  intense  igni- 
tion, and  just  in  the  condition  for  taking  up  oxygen.  This  flame 
is,  therefore,  reducing  in  its  effect,  and  is  technically  called  the 
reducing-^duvue.  The  substance  which  is  to  be  reduced  by  exposure 
to  this  flame,  should  be  completely  covered  up  by  the  luminous 
cone,  so  that  contact  with  the  air  may  be  entirely  avoided.  It  is 
to  be  observed  that,  whereas  to  produce  an  effective  oxidizing-flame 
a  strong  blast  of  air  is  desirable,  to  get  a  good  reducing-flame,  the  oper- 
ator should  blow  gently,  with  only  enough  force  to  divert  the  lamp- 
flame. 

Substances  to  be  heated  in  the  blowpipe-flame  are  supported,  some- 
times on  charcoal,  and  sometimes  on  platinum  foil  or  wire,  or  in 
platinum  spoons  or  forceps.  Charcoal  is  especially  suitable  for  a 
support  in  experiments  in  reduction.     With  reference  to  the  choice 


§§83,84.]  PLATINUM    UTENSILS.  l83 

of  charcoal  for  blowpipe  experiments,  see  §  83.     The  manner  of 
holding  the  blowpipe  is  illustrated  by  Fig.  28. 

83.  Platinum  Foil  and  Wire.    Pincers.  —  A  piece  of  platinum 
foil  about  1  ^  inches  long,  and  1  inch  wide 

will  be  suflBcient.     The  foil  should  be  at  ^^fif-  28. 

least  so  thick  that  it  does  not  crinkle 

when  wiped ;  and  it  is  more  economical 

to  get  foil  which  is  too  thick  than  too 

thin,  for  it  requires  frequent  cleaning. 

To  keep  foil  in  good  order  it  should  be 

frequently-  scoured  with  fine  moist  sand, 

and  in  case  the  foil  becomes  wrinkled,  it 

may  be  burnished  by  placing  it  upon  the 

bottom  of  an  inverted  agate  or  porcelain 

mortar  and  rubbing  it  strongly  with  the 

pestle. 

A  bit  of  platinum  wire,  not  stouter  than  the  wire  of  a  small  pin  and 
about  3  inches  long,  will  last  a  long  time  with  careful  usage.     It  may 
be  cleaned  by  long-continued  boiling  in  water.    A  small 
loop,  about  as  large  as  this  O,  should  be  bent  at  each  end    ^^S'  20. 
of  the  wire.  Q 

When  platinum  foil  is  to  be  heated,  it  may  be  held  at 
one  end  with  a  pair  of  the  small  steel  pincers  known  as 
jewellers'  tweezers.  A  piece  of  platinum  wire,  as  long  as 
the  one  above  •described,  can  be  held  in  the  fingers  with- 
out inconvenience,  for  platinum  is,  comparatively  speaking, 
a  bad  conductor  of  heat.  Pieces  of  wire,  too  short  to  be 
held,  may  be  made  serviceable  by  thrusting  one  end  of 
the  wire  into  the  end  of  a  glass  rod  or  closed  tube  which 
has  been  softened  in  the  blowpipe-flame. 

84.  Platinum  Crucibles.  —  For  several  of  the  oper- 
ations of  quantit-ative  analysis  as  now  practised,  platinum 
crucibles  are  indispensable,  and  though  not  absolutely  nec- 
essary for  the  profitable  study  of  qualitative  analysis,  one  Q 
of  these  vessels  will  often  be  found  convenient  by  the  stu- 
dent of  the  elements  of  analysis.  It  will  be  well,  therefore,  for  the 
student,  who  proposes  to  continue  his  chemical  studies  beyond  quali- 
tative analysis,  to  procure  a  platinum  crucible  once  for  all.  A  crucible 
of  the  capacity  of  about  20  cubic  centimeters  will  be  large  enough  for 
most  uses ;  it  should  be  cylindrical  rather  than  flaring,  and  should  be 


184  PLATINUM    UTENSILS.  [§§86,86. 

provided  with  a  loose  cover  in  the  form  of  a  shallow  dish.  For  the 
purposes  of  this  book,  however,  a  small  crucible  holding  7  or  8  centi- 
meters answers  every  purpose  and  a  cover  is  not  essential. 

No  other  metal,  and  no  mixture  of  substances  from  which  a  metal 
can  be  reduced,  must  ever  be  heated  in  a  platinum  crucible,  or  upon 
platinum  foil  or  wire,  for  platinum  forms  alloys  with  other  metals,  and 
these  alloys  are  much  more  fusible  than  platinum  itself.  If  once 
alloyed  with  a  baser  metal,  the  platinum  ceases  to  be  applicable  to  its 
peculiar  uses. 

Platinum  may  be  cleansed  by  boiling  it  in  either  nitric  or  hydrochloric 
acid,  by  fusing  acid  sulphate  of  sodium  upon  it,  or  by  scouring  it  with 
fine  sand.  Aqua  regia  and  chlorine- water  dissolve  platinum;  the 
sulphides,  cyanides,  and  hydrates  of  sodium  and  potassium,  when 
fused  in  platinum  vessels,  slowly  attack  the  metal. 

85.  Wash-bottle.  —  A  wash-bottle  is  a  flask  with  a  uniformly  thin 
bottom  closed  with  a  sound  cork  or  caoutchouc  stopper  through  which 
pass  two  glass  tubes,  as  shown  in  Fig.  30. 

The  outer  end  of  the  longer  tube  is  drawn  to  a 
Fig.  30.  moderately  fine  point.  A  short  bend  near  the  bottom 
of  this  longer  tube  in  the  same  plane  and  direction  as 
the  upper  bend  is  of  some  use,  because  it  enables  the 
operator  to  empty  the  flask  more  completely  by  inclin- 
ing it.  By  blowing  into  the  short  tube,  a  stream  of 
water  will  be  driven  out  of  the  long  tube  with  consid- 
erable force.  This  force  with  which  the  stream  is  pro- 
jected adapts  the  apparatus  to  removing  precipitates 
from  the  sides  of  vessels  as  well  as  to  washing  them 
on  filters.  For  use  in  analytical  operations,  it  is  often 
convenient  to  attach  a  caoutchouc  tube  12  or  15  c.  m. 
long  to  the  tube  through  which  the  air  is  blown ;  this 
flexible  tube  should  be  provided  with  a  glass  mouth- 
piece, consisting  of  a  bit  of  glass  tubing  about  3  c.  m.  long.  As  the 
wash-bottle  is  often  filled  with  hot  or  even  boiling  water,  it  may  be 
improved  by  binding  about  its  neck  a  ring  of  cork,  or  winding  the 
neck  closely  with  smooth  cord.  It  may  then  be  handled  without 
inconvenience  when  hot. 

The  method  of  making  a  wash-bottle  is  described  in  the  following 
paragraphs. 

86.  Glass  Tubing.  —  Two  qualities  of  glass  tubing  are  used  in 
chemical  experiments,  that  which  softens  readily  in  the  flame  of  a  gas- 


§§  87,  88.]      CUTTING  AND   CRACKING   GLASS.  185 

or  spirit-lamp,  and  that  which  fuses  with  extreme  difficulty  in  the  flame 
of  the  blast-lamp.  These  two  qualities  are  distinguished  by  the  terms 
soft  and  hard  glass.    Soft  glass  is  to  be  preferred  for  all  uses  except 


87654  3  2  1 

the  intense  heating,  or  ignition,  of  dry  substances.  Fig.  31  represents 
the  common  sizes  of  glass  tubing,  both  hard  and  soft,  and  shows  also 
the  proper  thickness  of  the  glass  walls  for  each  size.  The  numbers 
ranging  from  4  to  8  are  best  suited  for  use  in  qualitative  analysis. 

87.  Stirring- rods.  —  Cut  a  short  stick  of  glass  rod.  No.  8  or  7,  into 
pieces  four  or  five  inches  long  (see  the  next  paragraph),  and  round 
the  sharp  ends  by  fusion  in  the  blowpipe-flame. 

88.  Cutting  and  Cracking  Glass.  —  Glass  tubing  and  glass  rod 
must  generally  be  cut  to  the  length  required  for  any  particular  appa- 
ratus. A  sharp  triangular  file  is  used  for  this  purpose.  The  stick  of 
tubing,  or  rod,  to  be  cut  is  laid  upon  a  table,  and  a  deep  scratch  is 
made  with  the  file  at  the  place  where  the  fracture  is  to  be  made.  The 
stick  is  then  grasped  with  the  two  hands,  one  on  each  side  of  the 
mark,  while  the  thumbs  are  brought  together  just  at  the  scratch.  By 
pushing  with  the  thumbs  and  pulling  in  the  opposite  direction  with 
the  fingers,  the  stick  is  broken  squarely  at  the  scratch,  just  as  a  stick 
of  candy  or  dry  twig  may  be  broken.  The  sharp  edges  of  the  frac- 
ture should  invariably  be  made  smooth,  either  with  a  wet  file,  or  by 
softening  the  end  of  the  tube  or  rod  in  the  lamp  (App.,  §  89).  Tubes 
or  rods  of  sizes  4  to  8  inclusive  may  readily  be 

cut  in  this  manner ;  the  larger  sizes  are  divided  with  Figr.  32. 

more  difficulty,  and  it  is  often  necessary  to  make 
the  file- mark  both  long  and  deep.  An  even  fracture 
is  not  always  to  be  obtained  with  large  tubes.  The 
lower  ends  of  glass  funnels,  and  those  ends  of  gas 
delivery-tubes  which  enter  the  bottle  or  flask  in 
which  the  gas  is  generated,  should  be  filed  off,  or 
ground  off  on  a  grindstone,  obliquely  (Fig.  32),  to  facilitate  the  drop- 
ping of  liquids  from  such  extremities. 


rig*.  o;«s. 


186  MANIPULATION  OF  GLASS,  [§  89. 

In  order  to  cut  glass  plates,  the  glazier's  diamond  must  be  resorted 
to.  For  the  cutting  of  exceedingly  thin  glass  tubes  and  of  other  glass- 
ware, like  flasks,  retorts  and  bottles,  still  other  means  are  resorted  to, 
based  upon  the  sudden  and  unequal  application  of  heat.  The  process 
divides  itself  into  two  parts,  the  producing  of  a  crack  in  the  required 
place,  and  the  subsequent  guiding  of  this  crack  in  the  desired  direc- 
tion. To  produce  a  crack,  a  scratch  must  be  made  with  the  file,  and 
to  this  scratch  a  pointed  bit  of  red-hot  charcoal,  or  the  jet  of  flame 
produced  by  the  mouth-blowpipe,  or  a  very  fine  gas-flame,  or  a  red- 
hot  glass  rod  may  be  applied.  If  the  heat  does  not  produce  a  crack,  a 
wet  stick  or  file  may  be  touched  upon  the  hot  spot.  Upon  any  part  of 
a  glass  surface  except  the  edge,  it  is  not  possible  to  control  perfectly  the 
direction  and  extent  of  this  first  crack ;  at  an  edge  a  small  crack  may  be 
started  with  tolerable  certainty  by  carrying  the  file-mark  entirely  over 
the  edge.  To  guide  the  crack  thus  started,  a  pointed  bit  of  charcoal 
or  slow-match  may  be  used.  The  hot  point  must  be  kept  on  the  glass 
from  1  c.  m.  to  0.5  c.  m.  in  advance  of  the  point  of  the  crack.  The 
crack  will  follow  the  hot  point,  and  may  therefore  be  carried  in  any 
desired  direction.  By  turning  and  blowing  upon  the  coal  or  slow- 
match,  the  point  may  be  kept  sufficiently  hot.  Whenever  the  place 
of  experiment  is  supplied  with  common  illuminating  gas,  a  very  small 
jet  of  burning  gas  may  be  advantageously  substituted  for  the  hot  coal 
or  slow-match.  To  obtain  such  a  sharp  jet,  a  piece  of  hard  glass  tube, 
No.  4,  10  c,  m.  long,  and  drawn  to  a  very  fine  point  (App.,  §  89),  should 
be  placed  in  the  caoutchouc  tube  which  ordinarily  delivers  the  gas  to 
the  gas-lamp,  and  the  gas  should  be  lighted  at  the  fine  extremity. 
The  burning  jet  should  have  a  fine  point,  and  should  not  exceed 
1.5  c.  m.  in  length.  By  a  judicious  use  of  these  simple  tools,  broken 
tubes,  beakers,  flasks,  retorts  and  bottles  may  often  be  made  to  yield 
very  useful  articles  of  apparatus.  No  sharp  edges  should  be  allowed 
to  remain  upon  glass  apparatus.  The  durability  of  the  apparatus 
itself,  and  of  the  corks  and  caoutchouc  stoppers  and  tubing  used  with 
it,  will  be  much  greater,  if  all  sharp  edges  are  removed  with  the  file, 
or,  still  better,  rounded  in  the  lamp. 

89.  Bending  and  Closing  Glass  Tubes.  —  Tubing  of  sizes  4 
to  8  inclusive  can  generally  be  worked  in  the  common  gas-  or 
spirit-lamp;  for  larger  tubes  the  blast-lamp  is  necessary  (App.,  §  79). 
Glass  tubing  must  not  be  introduced  suddenly  into  the  hottest  part 
of  the  flame,  lest  it  crack.  Neither  should  a  hot  tube  be  taken  from 
the  flame  and  laid  at  once  upon  a  cold  surface.  Gradual  heating  and 
gradual  cooling  are  alike  necessary,  and  are  the  more  essential  the 


§89.]  MANIPULATION   OF  GLASS,  187 

thicker  the  glass ;  very  thin  glass  will  sometimes  bear  the  most 
sudden  changes  of  temperature,  but  thick  glass  and  glass  of  uneven 
thickness  absolutely  require  slow  heating  and  annealing.  When  the 
end  of  a  tube  is  to  be  heated,  as  in  rounding  sharp  edges,  more 
care  is  required  in  consequence  of  the  great  facility  with  which  cracks 
start  at  an  edge.  A  tube  should,  therefore,  always  be  brought  first 
into  the  current  of  hot  air  beyond  the  actual  flame  of  the  gas-  or  spirit- 
lamp,  and  there  thoroughly  warmed,  before  it  is  introduced  into  the 
flame  itself.  If  a  blast-lamp  is  employed,  the  tube  may  be  warmed  in 
the  smoky  flame  before  the  blast  is  turned  on,  and  may  subsequently 
be  annealed  in  the  same  manner ;  the  deposited  soot  will  be  burnt  off 
in  the  first  instance,  and  in  the  last  may  be  wiped  off  when  the  tube 
is  cold.  In  heating  a  tube,  whether  for  bending,  drawing  or  closing, 
the  tube  must  be  constantly  turned  between  the  fingers,  and  also  moved 
a  little  to  the  right  and  left,  in  order  that  it  may  be  uniformly  heated 
all  round,  and  that  the  temperature  of  the  neighboring  parts  may  be 
duly  raised.  If  a  tube  or  rod  is  to  be  heated  at  any  part  but  an  end, 
it  should  be  held  between  the  thumb  and  first  two  fingers  of  each 
hand  in  such  a  manner  that  the  hands  shall  be  below  the  tube  or  rod, 
with  the  palms  upward,  while  the  lamp-flame  is  between  the  hands. 
When  the  end  of  a  tube  or  rod  is  to  be  heated,  it  is  best  to  begin  by 
warming  the  tube  or  rod  about  2  c.  m.  from  the  end,  and  thence  to 
proceed  slowly  to  the  end. 

The  best  glass  will  not  be  blackened  or  discolored  during  heating. 
Blackening  occurs  in  glass  which,  like  ordinary  flint  glass,  contains 
lead  as  an  ingredient.  Glass  containing  much  lead  is  not  well  adapted 
for  chemical  uses.  The  blackening  may  sometimes  be  removed  by 
putting  the  glass  in  the  upper  or  outer  part  of  the  flame,  where  the 
reducing- gases  are  consumed,  and  the  air  has  the  best  access  to 
the  glass.  The  blackening  may  be  altogether  avoided  by  always 
keeping  the  glass  in  the  oxidizing  part  of  the  flame. 

Glass  begins  to  soften  and  bend  below  a  visible  red  heat.  The 
condition  of  the  glass  is  judged  of  as  much  by  the  fingers  as  the  eye  ; 
the  hands  feel  the  yielding  of  the  glass,  either  to  bending,  pushing  or 
pulling,  better  than  the  eye  can  see  the  change  of  color  or  form.  It 
may  be  bent  as  -soon  as  it  yields  in  the  hands,  but  can  be  drawn  out 
only  when  much  hotter  than  this.  Glass  tubing,  however,  should  not 
be  bent  at  too  low  a  temperature  ;  the  curves  made  at  too  low  a  heat 
are  apt  to  be  flattened,  of  unequal  thickness  on  the  convex  and  concave 
sides,  and  brittle. 

In  bending  tubing  to  make  gas  delivery- tubes  and  the  like,  attention 


188 


MANIPULATION   OF  GLASS. 


[§89. 


Pig.  33. 


should  be  paid  to  the  following  points  :  1st,  the  glass  should  be  equally 
hot  on  all  sides  ;  2d,  it  should  not  be  twisted,  pulled  out  or  pushed 
together  during  the  heating ;  3d,  the  bore  of  the  tube  at  the  bend 
should  be  kept  round,  and  not  altered  in  size ;  4th,  if  two  or  more 
bends  be  made  in  the  same  piece  of  tubing 
(Fig.  33,  a),  they  should  all  be  in  the  same 
/"r^  (C  a        ll    pl^-ne,  so  that  the  finished  tube  will  lie  flat 

i>       I  upon  the  level  table. 

U  When  a  tube  or  rod  is  to  be  bent  or  drawn 

J  f    close  to  its  extremity,  a  temporary  handle 

may  be  attached  to  it  by  softening  the  end 
of  the  tube  or  rod,  and  pressing  against  the  soft  glass  a  fragment  of 
glass  tube,  which  will  adhere  strongly  to  the  softened  end.  The  handle 
may  subsequently  be  removed  by  a  slight  blow,  or  by  the  aid  of  a  file. 
If  a  considerable  bend  is  to  be  made,  so  that  the  angle  between  the 
arms  will  be  very  small  or  nothing,  as  in  a  siphon,  for  example,  the 
curvature  cannot  be  well  produced  at  one  place  in  the  tube,  but  should 
be  made  by  heating,  progressively,  several  centimeters  of  the  tube,  and 
bending  continuously  from  one  end  of  the  heated  portion  to  the  other 
(Fig.  33,  6).  Small  and  thick  tube  maybe  bent  more  sharply  than 
large  or  thin  tube. 

A  lamp  for  bending  glass  tubing,  better  than  the  ordinary  form  of 
the  Bunsen  burner,  is  one  the  tube  of  which  is  flattened  out  so  as  to 
give  a  thin  but  broad  flame  of  the  same  character  as  the  ordinary 
lamp,  but  in  shape  more  like  a  bat-wing  burner. 
(See  Fig.  34.)  The  tube  is  placed  in  this  flame 
and  turned  round  and  round  until  it  reaches  the 
proper  temperature ;  it  is  then  withdrawn  from 
the  flame  and  bent.  In  this  way  a  regular  curve 
may  be  obtained  and  the  sides  of  the  tube  do  not 
collapse. 

In  order  to  draw  a  glass  tube  down  to  a  finer 
bore,  it  is  simply  necessary  to  thoroughly  soften  on 
all  sides  one  or  two  centimeters'  length  of  the  tube, 
and  then  taking  the  glass  from  the  flame,  pull  the 
parts  asunder  by  a  cautious  movement  of  the  hands. 
The  larger  the  heated  portion  of  glass,  the  longer 
will  be  the  tube  thus  formed.  Its  length  and  fineness  also  increase 
with  the  rapidity  of  motion  of  the  hands.  If  it  is  desirable  that  the 
finer  tube  should  have  thicker  walls  in  proportion  to  its  bore  than 
the  original  tube,  it  is  only  necessary  to  keep  the  heated  portion  soft 


Pig.  34. 


§90.]  MANIPULATION   OF  GLASS.  189 

for  two  or  three  minutes  before  drawing  out  the  tube,  pressing  the 
parts  slightly  together  the  while.  By  this  process  the  glass  will  be 
thickened  at  the  hot  ring. 

To  obtain  a  tube  closed  at  one  end,  it  is  best  to  take  a  piece  of 
tubing,  open  at  both  ends,  and  long  enough 
to  make  two  closed  tubes.  In  the  middle  of 
the  tube  a  ring  of  glass,  as  narrow  as  pos- 
sible, must  be  made  thoroughly  soft.  The 
hands  are  then  separated  a  little,  to  cause 
a  contraction  in  diameter  at  the  hot  and 
soft  part.    The  point  of  the  flame  must  now 

be  directed,  not  upon  the  narrowest  part  of  the  tube,  but  upon  what 
is  to  be  the  bottom  of  the  closed  tube.  This  point  is  indicated  by  the 
line  a  in  Fig.  35.  By  withdrawing  the  right  hand,  the  narrow  part 
of  the  tube  is  attenuated,  and  finally  melted  off,  leaving  both  halves 
of  the  original  tube  closed  at  one  end,  but  not  of  the  same  form ; 
the  right-hand  half  is  drawn  out  into  a  long  point,  the  other  is  more 
roundly  closed.  It  is  not  possible  to  close  handsomely  the  two  pieces 
at  once.  The  tube  is  seldom  perfectly  finished  by  the  operations ;  a 
superfluous  knob  of  glass  generally  remains  upon  the  end.  If  small 
it  may  be  got  rid  of  by  heating  the  whole  end  of  the  tube,  and  blowing 
moderately  with  the  mouth  into  the  open  end.  The  knob,  being  hot- 
ter, and  therefore  softer  than  any  other  part,  yields  to  the  pressure 
from  within,  spreads  out  and  disappears.  If  the  knob  is  large,  it  may 
be  drawn  off  by  sticking  to  it  a  fragment  of  tube,  and  then  softening 
the  glass  above  the  junction.  The  same  process  may  be  applied  to 
the  too  pointed  end  of  the  right-hand  half  of  the  original  tube,  or 
to  any  misshapen  result  of  an  unsuccessful  attempt  to  close  a  tube, 
or  to  any  bit  of  tube  which  is  too  short  to  make  two  closed  tubes. 
When  the  closed  end  of  a  tube  is  too  thin,  it  may  be  strengthened  by 
keeping  the  whole  end  at  a  red  heat  for  two  or  three  minutes,  turning 
the  tube  constantly  between  the  fingers.  It  may  be  said  in  general 
of  all  the  preceding  operations  before  the  lamp,  that  success  depends 
on  keeping  the  tube  to  be  heated  in  constant  rotation,  in  order  to 
secure  a  uniform  temperature  on  all  sides  of  the  tube. 

90.  Blowing  Bulbs.  —  Bulb-tubes,  like  the  one  represented  in 
Fig.  36,  are  employed  for  reducing  substances  capable  of  forming 
sublimates  upon  the  cold  walls  of  the  tube.  They  are  readily  made 
from  bits  of  tubing,  in  the  flame  of  Bunscn's  burner,  or  in  the  common 
blowpipe-flame. 

If  the  bulb  desired  is  large  in  proportion  to  the  size  of  the  tube  on 


190  •    CAOUTCHOUC.  [§91. 

which  it  is  to  be  made,  the  walls  of  the  tube  must  be  thickened  by 
rotation  in  the  flame  before  the  bulb  can  be  blown.    The  thickened 
portion  of  glass  is  then  to  be  heated  to  a  cherry -red,  suddenly  with- 
drawn from  the  flame,  and  expanded 
Fig.  36.  while  hot  by  steadily  blowing,  or 

rather  pressing,  air  into  the  tube 
with  the  mouth ;  the  tube  must  be 
constantly  turned  on  its  axis,  not 
only  while  in  the  flame,  but  also 
while  the  bulb  is  being  blown.  If 
too  strong  or  too  sudden  a  pressure 
be  exerted  with  the  mouth,  the  bulb  will  be  extremely  thin  and  quite 
useless.  By  watching  the  expanding  glass,  the  proper  moment  for 
arresting  the  pressure  may  usually  be  determined.  If  the  bulb 
obtained  be  not  large  enough,  it  may  be  reheated  and  enlarged  by 
blowing  into  it  again,  provided  that  a  sufficient  thickness  of  glass 
remain.  If  a  bulb  is  to  be  blown  in  the  middle  of  a  piece  of  tubing, 
the  thickening  is  effected  by  gently  pressing  the  ends  of  the  tube  to- 
gether while  the  glass  is  red-hot  in  the  place  where  the  bulb  is  to  be. 

It  is  sometimes  necessary  to  make  a  hole  in  the  side  of  a  tube  or 
other  thin  glass  apparatus.  This  may  be  done  by  directing  a  pointed 
flame  from  the  blast- lamp  upon  the  place  where  the  hole  is  to  be, 
until  a  small  spot  is  red-hot,  and  then  blowing  forcibly  into  one  end 
of  the  tube  while  the  other  end  is  closed  by  the  finger ;  at  the  hot 
spot  the  glass  is  blown  out  into  a  thin  bubble,  which  bursts  or  may 
be  easily  broken  off,  leaving  an  aperture  in  the  side  of  the  tube. 

It  is  hoped  that  these  few  directions  will  enable  the  attentive  student 
to  perform,  sufficiently  well,  all  the  manipulations  with  glass  tubes 
which  the  experiments  described  in  this  manual  require.  Much  practice 
will  alone  give  a  perfect  mastery  of  the  details  of  glass-blowing. 

91.  Caoutchouc.  —  Vulcanized  caoutchouc  is  a  most  useful  sub- 
stance in  the  laboratory,  on  account  of  its  elasticity  and  because  it 
resists  so  well  most  of  the  corrosive  substances  with  which  the  chemist 
deals.  It  is  used  in  three  forms:  (1)  in  tubing  of  various  diameters 
comparable  with  the  sizes  of  glass  tubing ;  (2)  in  stoppers  of  various 
sizes  to  replace  corks ;  (3)  in  sheets.  Caoutchouc  tubing  may  be 
used  to  conduct  all  gases  and  liquids  which  do  not  corrode  its  sub- 
stance, provided  that  the  pressure  under  which  the  gas  or  liquid  flows 
be  not  greater,  or  their  temperature  higher,  than  the  texture  of  the 
tubing  can  endure.  The  flexibility  of  the  tubing  is  a  very  obvious 
advantage  in  a  great  variety  of  cases.    Short  pieces  of  such  tubing,  a 


§92.]  CAOUTCHOUC.  —  CORKS.  191 

few  centimeters  in  length,  are  much  used,  under  the  name  of  con- 
nectors, to  make  flexible  joints  in  apparatus,  of  which  glass  tubing 
forms  part;  flexible  joints  add  greatly  to  the  durability  of  such 
apparatus,  because  long  glass  tubes  bent  at  several  angles  and  con- 
nected with  heavy  objects,  like  globes,  bottles  or  flasks  full  of  liquid, 
are  almost  certain  to  break  even  with  the  most  careful  usage;  gas 
delivery-tubes,  and  all  considerable  lengths  of  glass  tubing,  should 
invariably  be  divided  at  one  or  more  places,  and  the  pieces  joined 
again  with  caoutchouc  connectors.  The  ends  of  the  glass  tubing  to 
be  thus  connected  should  be  squarely  cut,  and  then  rounded  in  the 
lamp,  in  order  that  no  sharp  edges  may  cut  the  caoutchouc  ;  the  inter- 
nal diameter  of  the  caoutchouc  tube  must  be  a  little  smaller  than  the 
external  diameter  of  the  glass  tubes ;  the  slipping  on  of  the  connector 
is  facihtated  by  wetting  the  glass.  In  some  cases  of  delicate  quanti- 
tative manipulations,  in  which  the  tightest  possible  joints  must  be 
secured,  the  caoutchouc  connector  is  bound  on  to  the  glass  tube  with 
a  silk  or  smooth  linen  string  ;  the  string  is  passed  as  tightly  as  possible 
twice  round  the  connector  and  tied  with  a  square  knot ;  the  string 
should  be  moistened  in  order  to  prevent  it  from  slipping  while  the 
knot  is  tying. 

Caoutchouc  stoppers  are  much  more  durable  than  corks,  and  are  in 
every  respect  to  be  preferred,  if  of  proper  shape  and  good  quality. 
Caoutchouc  stoppers  can  be  bored,  like  corks  (see  the  next  section), 
by  means  of  suitable  cutters,  and  glass  tubes  can  be  fitted  into  the 
holes  thus  made  with  a  tightness  unattainable  with  corks ;  but  these 
stoppers  may  be  bought  already  provided  with  one,  two  and  three 
holes.  It  is  not  well  to  lay  in  a  large  stock  of  caoutchouc  stoppers,  for 
though  they  last  a  long  time  when  in  constant  use,  they  not  infre- 
quently deteriorate  when  kept  in  store,  becoming  hard  and  somewhat 
brittle  with  age. 

Pieces  of  thin  sheet  caoutchouc  are  very  conveniently  used  for 
making  tight  joints  between  large  tubes  of  two  different  sizes,  or 
between  the  neck  of  a  flask,  or  bottle,  and  a  large  tube  which  enters 
it,  or  between  the  neck  of  a  retort  and  the  receiver  into  which  it 
enters.  A  sufficiently  broad  and  long  piece  of  sheet  caoutchouc  is 
considerably  stretched,  wrapped  tightly  over  the  glass  parts  adjoining 
the  aperture  to  be  closed,  and  secured  in  place  by  a  string  wound 
closely  about  it  and  tied  with  a  square  knot. 

92.  Corks.  —  It  is  often  very  difficult  to  obtain  sound,  elastic  corks 
of  fine  grain  and  of  size  suitable  for  large  flasks  and  wide-mouthed 
bottles.    On  this  account,  bottles  with  mouths  not  too  large  to  be 


192 


CORKS. 


[§92. 


closed  with  a  cork  cut  across  the  grain,  should  be  chosen  for  chemical 
uses,  in  preference  to  bottles  which  require  large  corks  or  bungs  cut 
with  the  grain,  and  therefore  offering  continuous  channels  for  the 
passage  of  gases,  or  even  liquids.  The  kinds  sold  as  champagne  corks 
and  as  satin  corks  for  phials  are  suitable  for  chemical  use.  The  best 
corks  generally  need  to  be  softened  before  using  ;  this  softening  may 
be  effected  by  rolling  the  cork  under  a  board  upon  the  table,  or  under 
the  foot  upon  the  clean  floor,  or  by  gently  squeezing  it  on  all  sides 
with  the  well-known  tool  expressly  adapted  for  this  purpose,  and  thence 
called  a  cork-squeezer.    Steaming  also  softens  the  hardest  corks. 

Corks  must  often  be  cut  with  cleanness  and  precision  ;  a  sharp, 
thin  knife,  such  as  shoemakers  use,  is  desirable  for  this  purpose. 
When  a  cork  has  been  pared  down  to  reduce  its  diameter,  a  flat  file 
may  be  employed  in  finishing ;  the  file  must  be  fine  enough  to  leave 
a  smooth  surface  upon  the  cork ;  in  filing  a  cork,  a  cylindrical,  not  a 
conical,  form  should  be  aimed  at. 

In  boring  holes  through  corks  to  receive  glass  tubes,  a  hollow 
cylinder  of  sheet  brass  sharpened  at  one  end  is  a  very  convenient 
tool.  Fig.  37  represents  a  set  of  such  little  cylinders  of  graduated 
sizes,  slipping  one  within  the  other  into  a  very 
compact  form  ;  a  stout  wire,  of  the  same  length 
3  as  the  cylinders,  accompanies  the  set,  and 
serves  a  double  purpose,  —  passed  transversely 
through  two  holes  in  the  cap  which  terminates 
^^.  each  cylinder,  it  gives  the  hand  a  better  grasp 

[       I  of  the  tool  while  penetrating  the  cork ;   and 

I      I  when  the  hole  is  made,  the  wire  thrust  through 

^-r-r  an  opening  in  the  top  of  the  cap  expels  the 

U  little  cylinder  of  cork  which  else  would  remain 

in  the  cutting  cylinder  of  brass.  That  cutter, 
whose  diameter  is  next  below  that  of  the  glass 
tube  to  be  inserted  in  the  cork,  is  always  to  be 
selected,  and  if  the  hole  it  makes  is  too  small, 
a  round  file  must  be  used  to  enlarge  the  aper- 
ture ;  the  round  file,  also,  often  comes  in  play 
to  smooth  the  rough  sides  of  a  hole  made  by  a  dull  cork-borer.  A 
pair  of  small  calipers  is  a  very  convenient,  though  by  no  means  es- 
sential, tool  in  determining  which  size  of  cutter  to  employ.  A  flask 
which  presents  sharp  or  rough  edges  at  the  mouth  can  seldom  be 
tightly  corked,  for  the  cork  cannot  be  introduced  into  the  neck  without 
being  cut  or  roughened;  such  sharp  edges  must  be  rounded  in  the 


Pier.  37. 


§93.] 


GA  S-GENERA  TOES. 


193 


lamp.  In  thrusting  glass  tubes  through  bored  corks,  the  following 
directions  are  to  be  observed :  (1)  The  end  of  the  tube  must  not  pre- 
sent a  sharp  edge  capable  of  cutting  the  cork.  (2)  The  tube  should  be 
grasped  very  close  to  the  cork,  in  order  to  escape  cutting  the  hand 
which  holds  the  cork,  should  the  tube  break ;  by  observing  this  pre- 
caution, the  chief  cause  of  breakage,  viz.  irregular  lateral  pressure, 
will  be  at  the  same  time  avoided.  (3)  A  funnel-tube  must  never  be 
held  by  the  funnel  in  driving  it  through  a  cork,  nor  a  bent  tube  grasped 
at  the  bend,  unless  the  bend  comes  immediately  above  the  cork. 
(4)  If  the  tube  goes  very  hard  through  the  cork,  the  application  of  a 
little  soap  and  water  will  facilitate  its  passage,  but  if  soap  is  used,  the 
tube  can  seldom  be  withdrawn  from  the  cork  after  the  latter  has 
become  diy.  (5)  The  tube  must  not  be  pushed  straight  into  the  cork, 
but  screwed  in,  as  it  were,  with  a  slow  rotary  as  well  as  onward 
motion.  Joints  made  with  corks  should  always  be  tested  before  the 
apparatus  is  used,  by  blowing  into  the  apparatus,  and  at  the  same 
time  stopping  up  all  legitimate  outlets.  Any  leakage  is  revealed  by 
the  disappearance  of  the  pressure  created.  To  the  same  end,  air  may 
be  sucked  out  of  an  apparatus  and  its  tightness  proved  by  the  per- 
manence of  the  partial  vacuum.  To  attempt  to  use  a  leaky  cork  is 
generally  to  waste  time  and  labor,  and  to  insure  the  failure  of  the 
experiment. 

93.  Gas-bottle.  —  Fig.  38  represents  a  gas-bottle  fitted  for  evolv- 
ing sulphuretted  hydrogen,  carbonic  acid  and  other  gases  which  can 
be  prepared  without  heat.  A  straight  glass  tube  of 
convenient  length  is  slipped  into  the  caoutchouc 
connector  at  the  right  to  carry  the  gas  into  the 
solution  to  be  tested.  The  neck  of  the  bottle 
should  be  rather  narrow,  since  it  is  difficult  to 
obtain  tight  stoppers  for  bottles  with  wide  mouths, 
but  must  nevertheless  be  wide  enough  to  admit  a 
cork,  or  better  a  caoutchouc  stopper,  capable  of 
carrying  both  the  delivery  and  the  thistle-tubes. 

To  prepare,  for  example,  sulphuretted  hydrogen 
gas,  put  a  tablespoonful  of  fragments  of  sulphide  of 
iron  in  the  bottom  of  the  bottle,  replace  the  cork 
with  its  tubes,  and  press,  or  rather  twist,  it  tightly 
into  the  neck  of  the  bottle ;  pour  in  enough  water 
through  the  thistle-tube  to  seal  the  lower  end  of 
that  tube,  and  finally  as  much  concentrated  sulphuric  acid  as  would 
be  equal  to  a  tenth  or  a  twelfth  of  the  volume  of  the  water. 


194 


GAS-GENEBATORS. 


[§94. 


At  the  start  it  is  well  thus  to  mix  strong  acid  with  the  water  in  the 
bottle,  for  the  heat  generated  by  the  union  of  the  two  liquids  serves  to 
warm  the  apparatus,  and  to  facilitate  the  decomposition  of  the  sul- 
phide of  iron ;  but  it  must  be  remembered  that  strong  sulphuric  acid 
is  by  itself  unfit  for  generating  sulphuretted  hydrogen,  and  that  the 
evolution  of  gas  would  be  checked  if  much  of  it  were  added.  When 
the  flow  of  gas  ceases,  pour  a  small  portion  of  dilute  sulphuric  acid 
into  the  thistle-tube,  and  repeat  this  operation  as  often  as  may  be 
necessary  to  maintain  a  constant  stream  of  gas.  Dilute  acid  fit  for 
this  purpose  may  be  prepared  by  mixing  1  volume  of  strong  sulphuric 
acid  with  14  volumes  of  water  ;  —  the  water  should  be  well  stirred  and 
the  acid  poured  into  it  in  a  fine  stream. 

In  precipitating  the  members  of  Classes  II  and  III  with  sulphu- 
retted hydrogen,  the  gas  delivery-tube  should  not  dip  deeper  than 
about  an  inch  beneath  the  surface  of  the  liquid  in  the  beaker.  A 
rapid  current  of  gas  is  useless  and  wasteful.  The  best  method  of 
operating  is  to  pour  dilute  sulphuric  acid  into  the  thistle- tube  in  such 
quantity  that  the  bubbles  of  gas  may  follow  one  another  slowly  enough 
to  be  counted  without  effort. 

94.  Self- regulating  Gas- generator.  —  An  apparatus  which  is 
always  ready  to  deliver  a  constant  stream  of  sulphuretted  hydrogen, 
and  yet  does  not  generate  the  gas  except 
when  it  is  immediately  wanted  for  use, 
is  a  great  convenience  in  an  active  labo- 
ratory. The  same  remark  applies  to  the 
two  gases,  hydrogen  and  carbonic  acid, 
which  are  likewise  used  in  considerable 
quantities  in  quantitative  analysis,  and 
which  can  be  conveniently  generated  in 
precisely  the  same  form  of  apparatus 
which  is  advantageous  for  sulphuretted 
hydrogen.  Such  a  generator  may  be 
made  of  divers  dimensions.  The  fol- 
lowing directions,  with  the  accompanying 
figure  (Fig.  39),  will  enable  the  student 
to  construct  an  apparatus  of  convenient 
size.  Procure  a  glass  cylinder  20  or  25 
c,  m,  in  diameter  and  30  or  35  c.  m.  high  ; 
ribbed  candy  jars  are  sometimes  to  be  had  of  about  this  size ;  pro- 
cure also  a  stout  tubulated  bell-glass  10  or  12  c.  m.  wide  and  5  or  7  c.  m. 
shorter  than  the  cylinder.    Get  a  basket  of  sheet-lead  7.6  c.  m.  deep 


Fig.  39. 


§  94.]  GAS-GEN EBATOBS.  195 

and  2.5  c.  m.  narrower  than  the  bell-glass,  and  bore  a  number  of  small 
holes  in  the  sides  and  bottom  of  this  basket.  Cast  a  circular  plate  of 
lead  7  m.  m.  thick  and  of  a  diameter  4  c.  m.  larger  than  that  of  the 
glass  cylinder;  on  what  is  intended  for  its  under  side  solder  three 
equidistant  leaden  strips,  or  a  continuous  ring  of  lead,  to  keep  the 
plate  in  proper  position  as  a  cover  for  the  cylinder.  Fit  tightly  to 
each  end  of  a  good  brass  gas-cock  a  piece  of  brass  tube  8  c.  m.  long, 
1.5  to  2  cm.  wide,  and  stout  in  metal.  Perforate  the  centre  of  the 
leaden  plate,  so  that  one  of  these  tubes  will  snugly  pass  through  the 
orifice,  and  secure  it  by  solder,  leaving  5  c.  m.  of  the  tube  projecting 
below  the  plate.  Attach  to  the  lower  end  of  this  tube  a  stout  hook  on 
which  to  hang  the  leaden  basket.  By  means  of  a  sound  cork  and 
common  sealing-wax,  or  a  cement  made  of  oil  mixed  with  red  and 
white  lead,  fasten  this  tube  into  the  tubulure  of  the  bell-glass  air-tight, 
and  so  firmly  that  the  joint  will  bear  a  weight  of  several  pounds. 
Hang  the  basket  by  means  of  copper  wire  within  the  bell  5  c.  m.  above 
the  bottom  of  the  latter.  To  the  tube  which  extends  above  the '  stop- 
cock attach  by  a  good  cork  the  neck  of  a  tubulated  receiver  of  100  or 
150  c.  c.  capacity,  the  interior  of  which  has  been  loosely  stuffed  with 
cotton.  Into  the  second  tubulure  of  the  receiver  fit  tightly  the  delivery- 
tube  carrying  a  caoutchouc  connector;  into  this  connector  can  be 
fitted  a  tube  adapted  to  convey  the  gas  in  any  desired  direction. 
When  many  persons  use  the  same  generator,  each  person  must  bring 
his  own  tube. 

To  charge  the  apparatus,  fill  the  cylinder  with  dilute  acid  to  within 
10  or  12  c.  m.  of  the  top,  fill  the  basket  with  fragments  of  sulphide  of 
iron,  hang  the  basket  in  the  bell,  and  put  the  bell-glass  full  of  air  into 
its  place  with  the  stop- cock  closed.  On  opening  the  cock,  the  weight 
of  the  acid  expels  the  air  from  the  bell,  the  acid  comes  in  contact  with 
the  solid  in  the  basket,  and  a  steady  supply  of  gas  is  generated  un  I 
either  the  acid  is  saturated  or  the  solid  dissolved  ;  if  the  cock  1 . ) 
closed,  the  gas  accumulates  in  the  bell,  and  pushes  the  acid  below  t?  ) 
basket  so  that  all  action  ceases.  In  cold  weather  the  apparatus  mu  *". 
be  kept  in  a  warm  place.  For  generating  sulphuretted  hydroger, 
sulphuric  acid  diluted  with  14  parts  of  water  is  used  ;  for  hydro- 
gen, zinc  and  sulphuric  acid  diluted  with  4  or  5  parts  of  water; 
while  for  carbonic  acid,  marble  and  hydrochloric  acid  diluted  with  2 
or  3  parts  of  water  should  be  taken. 

Many  forms  of  self -regulating  gas- generators  can  be  obtained  of 
dealers  in  chemical  apparatus  :  that  known  as  "  Kipp's  Generator  "  is 
excellent  for  use  in  small  laboratories. 


196  MOBTABS.  [§95. 

95.  Mortars.  —  Whenever  the  substance  to  be  analyzed  occurs  in 
the  form  of  large  pieces  or  coarse  powder,  it  should,  as  a  general  rule, 
be  pulverized  by  mechanical  means  before  subjecting  it  to  the  action 
of  solvents.  Mortars  of  iron,  steel,  agate  or  porcelain  are  used  for 
this  purpose,  according  to  the  character  of  the  substance  to  be 
powdered. 

An  iron  mortar  is  useful  for  coarse  work  and  for  effecting  the  first 
rough  breaking  up  of  substances  which  are  subsequently  powdered  in 
the  agate  or  porcelain  mortar.  If  there  be  any  risk  of  fragments 
being  thrown  out  of  the  mortar,  it  should  be  covered  with  a  cloth  or 
piece  of  stiff  paper,  having  a  hole  in  the  middle  through  which  the 
pestle  may  be  passed.  Instead  of  the  common  iron  mortar  a  small 
steel  mortar,  of  the  kind  called  diamond  mortars  by  dealers  in  chemical 
ware,  may  be  used  for  crushing  minerals.  Pieces  of  stone,  minerals 
and  lumps  of  brittle  metals  may  be  safely  broken  into  fragments 
suitable  for  the  mortar  by  wrapping  them  in  strong  paper,  laying  them 
so  enclosed  upon  an  anvil,  and  striking  them  with  a  heavy  hammer 
The  paper  envelope  retains  the  broken  particles  which  might  otherwise 
fly  about  in  a  dangerous  manner,  and  be  lost. 

The  best  porcelain  mortars  are  those  known  by  the  name  of  Wedge- 
wood- ware,  but  there  are  many  cheaper  substitutes.  Porcelain  mortars 
will  not  bear  sharp  and  heavy  blows;  they  are  intended  rather  for 
grinding  or  triturating  saline  substances  than  for  hammering ;  the 
pestle  may  either  be  formed  of  one  piece  of  porcelain,  or  a  piece  of 
porcelain  cemented  to  a  wooden  handle  ;  the  latter  is  the  less  desira- 
ble form  of  pestle.  Unglazed  porcelain  mortars  are  to  be  preferred. 
In  selecting  mortars,  the  following  points  should  be  attended  to : 
1st,  the  mortar  should  not  be  porous ;  it  ought  not  to  absorb  strong 
acids  or  any  colored  fluid,  even  if  such  liquids  be  allowed  to  stand  for 
hours  in  the  mortar ;  2d,  it  should  be  very  hard,  and  its  pestle  should 
be  of  the  same  hardness  ;  3d,  it  should  be  sound ;  4th,  it  should  have 
a  lip  for  the  convenience  of  pouring  out  liquids  and  fine  powders.  As 
a  rule,  porcelain  mortars  will  not  endure  sudden  changes  of  tempera- 
ture. Tliey  may  be  cleaned  by  rubbing  in  them  a  little  sand  soaked  in 
nitric  or  sulphuric  acid,  or  if  acids  are  not  appropriate,  in  caustic  soda. 

Agate  mortars  are  only  intended  for  trituration ;  a  blow  would 
break  them.  They  are  exceedingly  hard,  and  impermeable.  The 
material  is  so  precious  and  so  hard  to  work,  that  agate  mortars  are 
always  small.  The  pestles  are  generally  inconveniently  short,  —  a 
difficulty  which  may  be  remedied  by  fitting  the  agate  pestle  into  a 
wooden  handle. 


§96.]  SPATULA.  197 

In  all  grinding  operations  in  mortars,  whether  of  porcelain  or  agate, 
it  is  expedient  to  put  only  a  small  quantity  of  the  substance  to  be 
powdered  into  the  mortar  at  once.  The  operation  of  powdering  will 
be  facilitated  by  sifting  the  matter  as  fast  as  it  is  powdered,  returning 
to  the  mortar  the  particles  which  are  too  large  to  pass  through  the 
sieve. 

96.  Spatulae.  —  For  transferring  substances  in  powder,  or  in  small 
grains  or  crystals,  from  one  vessel  to  another,  spatulae  and  scoops 
made  of  horn  or  bone  are  convenient  tools.  A  coarse  bone  paper- 
knife  makes  a  good  spatula  for  laboratory  use.  Cards,  free  from 
glaze  and  enamel,  are  excellent  substitutes  for  spatulae. 


INDEX. 


Acetate  of  lead,  as  reagent,  156. 

sodium,  as  reagent,  154. 
Acetates,  tests  for,  103. 
Acetic  acid,  as  reagent,  150. 
Acid  solutions,  122,  124. 
Alcohol,  as  reagent,  158. 
Alkaline  solutions,  122. 
Alloys,  treatment  of,  141. 
Aluminates,  precipitated  with  Class 

IV,  46. 
Aluminum,  confirmatory  test  for,  50. 
a  member  of  Class  IV, 

12,46. 
precipitated  as  hydrate, 

12,46. 
presence  of,  indicated,  56. 
Ammonia-water,  as  reagent,  151. 
Ammonium  salts,  testing  for,  109. 

indicated,  109. 
Antimony,  confirmatory  tests  for,  37. 
converted  into  an  insolu- 
ble oxide  by  HNO3,  143. 
see  sulphide  of. 
globule  brittle,  112. 
a  member  of  Class  III, 

11,  32. 
precipitated  as  sulphide, 

11,  32. 
presence  of,  indicated,  42, 

125. 
spots  distinguished  from 

arsenic  spots,  37. 
trioxide  of,  as  sublimate, 
109. 
Aqua  regia,  how  prepared,  150. 

its  use  as  a  solvent,  120. 
Argand  spirit-lamp,  178. 
Arseniates,  test  for,  92. 


Arsenic,  confirmatory  test  for,  35. 

a  member  of  Class  III,  11, 

32. 
presence  of,  indicated,  30, 

42,  113. 
see  sulphide  of. 
separation  a&  sulphide,  11, 

32. 
as  a  sublimate,  110. 
Arsenic  acid,  tests  for,  35,  92. 
Arsenious  acid,  distinguished  from 

arsenic  acid,  92. 
Arsenious  oxide  as  sublimate,  110. 
Arsenites,  tests  for,  92. 
Ash  of  charcoal,  112. 

Barium,  a  member  of  Class  VI,  15. 
precipitated  as  carbonate, 

05. 
precipitated   as   chromate, 

66. 
salts  soluble  in  ammoniacal 

solutions,  81. 
test  for  certain  classes  of 
salts,  79. 
Beakers,  165. 

Biborate  of  sodium  (borax),  as  re- 
agent, 154. 
Bichromate  of  potassium,  as  reagent, 

154. 
Bismuth,  confirmatory  test  for,  26. 
globule  brittle,  112. 
a  member  of  Class  II,  11,  23. 
precipitated  as  hydrate,  26. 
precipitated    as    sulphide, 

11,  23. 
presence  of,  indicated,  112, 
125. 

199 


200 


INDEX. 


Bisulphide  of  carbon,  as  reagent,  158. 
Blast-lamps,  174. 
Blowing  bulbs,  189. 
Blowpipe,  180. 

how  to  use,  181. 
lamp,  181. 
Boracic  acid,  precipitated  from  an  al- 
kaline solution,  123. 
tests  for,  96. 
Borates,  tests  for,  %. 
Borax-bead,  how  to  dilute,  133. 
how  to  make,  133. 
Bottles,  how  to  handle,  163. 
Bromides,  tests  for,  98, 100. 
Bromine,  tests  for,  98,  100. 
Bunsen's  burner,  173. 

filter-pump,  172. 

Cadmium,  a  member  of  Class  II,  11. 
precipitated  as  sulphide, 

11,  28. 
presence  of,  indicated,  30, 

125. 
separation  of,  28. 
Calcium,  a  member  of  Class  VI,  14. 
precipitated  as  carbonate, 

14,65. 
precipitated  as  oxalate,  67. 
test  for  certain  classes  of 
salts,  82. 
Caoutchouc  stoppers,  190. 

tubing,  191. 
Carbonate  of  ammonium,  as  reagent, 

152. 
Carbonate   of   sodium,  as   reagent, 

how  purified,  153. 
Carbonates,  tests  for,  88.  * 
Carbonic  acid,  tests  for,  88. 
Charcoal  for  blowpipe  use.  111. 
Chlorates,  tests  for,  103. 
Chloride  of  ammonium,  as  reagent, 
152. 
of  ammonium,  uses  of,  13, 
56,  69. 
Chloride  of  barium,  as  reagent,  156. 
Chloride  of  calcium,  as  reagent,  how 

prepared,  155. 
Chloride  of  lead,  solubility  of,  11. 
Chloride    of    mercury,   as   reagent, 
157. 


Chloride  of  silver  soluble  in  ammo- 
nia-water, 21. 
Chlorides,  tests  for,  84,  98. 
Chlorine,  tests  for,  98. 
Chlorine  water,  as  reagent,  158. 
Chromate  of  lead,  a  test  for  chro- 
mium, 49. 
Chromate  of  potassium,  as  reagent, 

154. 
Chromates,  barium  test  for,  80. 

reduction  of,  by  HjS,  31, 

91. 
tests  for,  91. 
Chrome  iron  ore,  hard  to  decompose. 

133. 
Chromic  oxide,  hard  to  decompose, 

133. 
Chromites,  precipitated  with  Class 

IV,  46. 
Chromium,  a  member  of  Class  IV, 
12,  46. 
detected  as  chromate  of 

sodium,  49. 
gives     a    green    borax 

bead,  133. 
precipitated  as  hydrate, 

12,46. 
presence   of,   indicated, 
56. 
Class,  the  term  defined,  0. 
Class  I,  defined,  6. 

how  to  precipitate,  19. 
Class  II,  defined,  7. 

how  to  precipitate,  23. 
Class  III,  defined,  7. 

precipitation  of,  32. 
Class  IV,  defined,  12. 

how  to  precipitate,  47,  55. 
salts  precipitated  with,  46. 
Class  V,  defined,  13. 

how  to  precipitate,  58,  63. 
Class  VI,  defined,  14. 

how  to  precipitate,  65,  69. 
Class  VII,  defined,  15. 

how  isolated,  15,  73. 
Clay  chimney  for  Bunsen's  burner, 

178. 
Closed-tube  test,  106. 
Cobalt,  member  of  Class  V,  14,  58. 
blowpipe  test  for,  61. 


INDEX. 


201 


Cobalt,  confirmatory  test  for,  62. 

precipitated  as  sulphide,  13, 

58. 
presence   of,    indicated,    63, 
115. 
Copper,  member  of  Class  II,  11,  23. 
confirmatory  test  for,  27. 
gives  blue  solutions,  26. 
globule  described,  112,  113. 
precipitated  as  sulphide,  11, 

23. 
presence  of,  indicated,  31. 
Cork-cutters,  192. 
Corks,  191. 

to  force  tubes  through,  193. 
Cyanide  of  mercury,  to  detect  cyano- 
gen in,  89. 
Cyanide  of  potassium,  reagent,  154. 
Cyanides,  tests  for,  88,  89. 
Cyanogen,  tests  for,  88,  89. 

Deflagration,  139. 
Dissolving  in  acids,  118. 
in  water,  117. 

Effervescence,  what  it  indicates, 

87. 
Elements,  identified  by  compounds,  2. 

treated  of,  1. 
Etching  glass,  a  test  for  fluorine,  97. 
Evaporation  test  applied  to  a  liquid, 

145. 

Ferri-  and  Fbrro-cyanide  of  po- 
tassium, as  reagents,  154. 
Ferric  chloride,  as  reagent,  156. 
Filtering,  165. 
Filter-stand,  167. 
Filtration,  rapid,  167. 
Flasks,  164. 
Fluoride  of  silicon,  a  test  for  fluorine 

and  silicon,  97. 
Fluorides,  tests  for,  96. 
Folding  filters,  16(5. 
Funnels,  165. 

Fused  minerals,  how  treated,  135. 
Fusion  with  acid  sulphate  of  sodium, 
139. 

with  CaCOs  and  NH4CI,  139. 

with  carbonate  of  sodium,  134. 


Fusions  in  platinum  crucibles,  114. 

Gas  bottle,  193. 

Gas-generators,  self-regulating,  194. 
General  reagent,  defined,  7. 
General  reagents  for  acids,  78. 

to  be  used  in  a  cer- 
tain order,  16. 
Glass,  bending  and  closing  tubes,  186. 

cutting  and  cracking,  185. 

tubing,  184. 
Gold,  globule  described,  112. 

insoluble  in  HNO3,  142. 

a  member  of  Class  III,  11,  39. 

presence  of,  indicated,  43. 

confirmatory  test  for,  41. 

purple  of  Cassius,  test  for,  143. 

Hydrates,  presence  of,  indicated, 

104. 
Hydrochloric  acid,  as  reagent,  149. 
its  application  as 
a  solvent,  118. 
Hydrogen,  its  presence  inferred,  76. 
Hyposulphites  (thiosulphates),  tests 
for,  90. 

Indigo  solution,  how  prepared,  157. 
Insoluble  substances,  130. 
Iodides,  tests  for,  99,  100. 
Iodine,  tests  for,  99,  100. 
lodo-starch  paper,  155. 
Iron,  discrimination  between  ferrous 
and  ferric  salts,  54. 

to  be  converted  into  ferric  salt, 
54. 

a  member  of  Class  IV,  12,  46. 

precipitated  as  hydrate,  12,  46. 

presence  of,  indicated,  56. 

Prussian  blue,  test  for,  51. 

reaction  in  borax  bead,  134. 
Iron  stand,  178. 

Labelling,  importance  of,  9. 

Lamps,  173. 

Lead,  belongs  to  two  classes,  11. 

globule  described,  112. 

a  member  of  Class  I,  7,  19. 

a  member  of  Class  II,  11,  23. 

paper,  how  prepared,  156. 


202 


INDEX. 


Lead,  precipitated  as   sulphide,  11, 
23. 
precipitation  as  chloride,  19. 
precipitation  as  sulphate,  20, 

26. 
presence  of,  indicated,  30. 
Lime-water,  as  reagent,  155. 
Liquids  to  be    tested  with    litmus, 

145. 
Litmus  paper,  how  prepared,  157. 

Magnesium,  as   member   of   Class 
VII,  15,  71. 
precipitated  as   phos- 
phate   of    Mg    and 
NH4,  15,  71. 
separation  as  oxide,  73. 
mixture,  as    reagent, 
156. 
Manganate  of  sodium,  51. 
Manganese,  conhrmatory  test,  51. 

precipitated  with  Class 

IV,  47. 
precipitation  of,  as  hy- 
drate, 59. 
presence  indicated,  63. 
Mercuric  chloride,  as  reagent,  157. 
Mercurous    chloride,   reaction    with 

ammonia-water,  21. 
Mercury,  belongs  to  two  classes,  11. 
compounds  as  sublimates, 

109. 
member  of  Class  I,  7,  19. 
member  of  Class  II,  11,  23. 
precipitation    as    subchlo- 

ride,  19. 
presence  of,  indicated,  30. 
reduction  of  the  metal  in  a 

closed  tube,  21. 
reduction  of  the  metal  on 

copper,  25. 
separation  as  sulphide,  11, 

23. 
as  a  sublimate,  109. 
Metallic  elements,  seven  classes  of,  17. 
globules  described,  112. 
globules  tested  in  oxidizing 
flame,  113. 
Metals,  action  of  HNO3  on,  141. 
used  in  the  arts,  141. 


Molybdate  of  ammonium,  a  test  for 
phosphates,  93. 
of  ammonium,  as  reagent, 
how  prepared,  152. 

Mortars,  196. 

Neutral  solutions,  122. 
Nickel,  blowpipe  test  for,  61. 

member  of  Class  V,  14,  58. 
precipitated  as  cyanide,  61. 
precipitated  as  hydrate,  61. 
precipitated  as  sulphide,  14, 

58. 
presence   of,    indicated,  63, 
115. 
Nitrate  of  barium,  as  reagent,  156. 
when  used,  82. 
of  cobalt,  as  reagent,  156. 
of  potassium,  as  reagent,  155. 
of  silver,  as  reagent,  155. 
of  sodium,  as  reagent,  154. 
Nitrates,  tests  for,  102. 
Nitric  acid,  action  on  metals,  121. 
dilute,  as  reagent,  150. 
strong,  as  reagent,  150. 
tests  for,  102. 
when  to  be  used  as  a 
solvent,  118,  119,  141. 
Nitrite  of  potassium,  as  reagent,  how 

prepared,  155. 
Nitrogen  peroxide,  108. 
Non-metallic  elements,  how  detected, 
76. 

Organic  matter,  detection  of,  107. 
how    destroyed, 
115. 
Organic  substances  hinder  the  pre- 
cipitation of  Class  IV,  57. 
Oxalate  of  ammonium,  reagent,  152. 
Oxalates  converted  into  carbonates, 
68. 
tests  for  95. 
Oxalic  acid  as  a  sublimate,  109. 
as  reagent,  150. 
tests  for,  95. 

oxides,    recognition    of, 
104. 
Oxide  of  manganese,  as  reagent,  156. 
Oxide  of  mercury,  as  reagent,  157. 
Oxidizing  blowpipe-flame,  182. 


INDEX. 


203 


Oxygen,  how  recognized,  108. 

its  presence  inferred,  76. 

Peroxides,  how  recognized,  104. 
Phosphate  of  calcium,  presence  of, 
indicated,  50. 
of  sodium,  as  reagent,  154. 
Phosphates,  precipitated  with  Class 
IV,  46. 
tests  for,  93. 
Phosphoric  acid,  tests  for,  93. 
Pincers,  183. 
Platinic  chloride,  as  reagent,  how 

prepared,  157. 
Platinum,  a  member  of  Class  III,  11, 
32. 
crucibles,  183. 
foil,  183. 

insoluble  in  HNO3,  142. 
presence  of,  indicated,  43. 
test  for,  40,  143. 
wire,  183. 
Porcelain  crucibles,  172. 

dishes,  172. 
Potassium,  precipitated   as   chloro- 
platinate,  73. 
flame-test  for,  72. 
a  member  of  Class  VII, 
15,  71. 
Precipitates   compacted   by  boiling 

and  shaking,  58. 
Preliminary  examination  of  a  liquid, 

99. 
Preliminary  treatment,  106. 

of  a  pure  metal  or  alloy, 
141. 
Prussian  blue,  a  test  for  iron,  51. 
Pulverizing,  196. 

Qualitative  analysis  defined,  1. 

Reagent  bottles,  162. 
Reagents,  149-158. 
Reducing  blowpipe-flame,  182. 
Reduction  test.  111. 

how  to  perform  with 

delicacy,  114. 
to  be  applied  to  in- 
soluble substances, 
131. 


Richards's  aspirator,  172. 

Salts,  kinds  of,  considered,  78. 

soluble  in  water,  120. 
Sand-bath,  179. 
Separation  of  two  elements,  5. 
Silicates,   alkaline,  decomposed   by 
acids,  96,  123. 
decomposed    by    chloride 
of  ammonium,  139. 
Silicates,  tests  for,  96. 

the  commonest  of  insoluble 
substances,  138. 
Silicic  acid,  precipitated  from  an  al- 
kaline solution,  123. 
Silver,  a  member  of  Class  I,  6, 19. 
globule  described,  112. 
precipitated      by     reducing 

agents,  86. 
precipitation  as  chloride,  19. 
salts,  insoluble  in  dilute  nitric 

acid,  85. 
salts,  sundry,  colors  of,  85. 
see  chloride  of. 
test   for   certain   classes    of 
salts,  83. 
Slaked  lime,  as  reagent,  155. 
Sodium,   crystallization    of   chloro- 
platinate  of,  73. 
flame-test  for,  72. 
a  member  of  Class  VII,  15, 

71. 
hydrate  as  reagent,  152. 
Solubilities,  table  of,  128,  129. 
Solution  of  indigo,  as  reagent,  157. 
Solutions    of    known    composition, 

159-161. 
Solvents,  the  order  of  use,  117. 
Spatulae,  197. 

Special  tests  for   non-metallic   ele- 
ments, 87-104. 
Stannous  chloride,  as  reagent,  how 

prepared,  156. 
Starch  paste,  how  prepared,  158. 
Starch-test  for  bromine,  98. 

iodine,  99. 
Stirring-rods,  185. 
Stoppers,  stuck,  how  to  loosen,  163. 
Strontium,  a  member  of  Class  VI,  15, 
65. 


204 


INDEX. 


Strontium,  precipitated  as  carbonate, 
15,66. 
precipitated  as  sulpliate, 
67. 
Sublimates  on  charcoal  while  reduc- 
ing metals,  113. 
Sulphate  of  copper,  as  reagent,  156. 
of  sodium,  acid,  how  pre- 
pared, 154. 
Sulphates,  barium  test  for,  81. 
how  to  detect,  93. 
insoluble,  reduced  to  sul- 
phides, 132. 
Sulphate  of  potassium,  as  reagent, 

how  prepared,  154. 
Sulphide  of  ammonium,  as  reagent, 

how  prepared,  151. 
Sulphide  of  arsenic,  oxidation  of,  34, 

41. 
Sulphide  of  sodium,  as  reagent,  how 

prepared,  153. 
Sulphide  of  tin,  oxidation  of,  34. 
Sulphides,  tests  for,  89. 
Sulphides  of  arsenic,  as  sublimates, 

110. 
Sulphites,  tests  for,  90. 
Sulphur,  as  a  sublimate,  110. 
Sulphuretted  hydrogen,  decomposed 

by  oxidizing  agents,  30. 
Sulphuretted    hydrogen,    how   pre- 
pared, 151. 
Sulphuretted  hydrogen,  how  to  em- 
ploy it,  8,  23. 
Sulphuretted  hydrogen,  necessity  of 

expelling,  54. 
Sulphuretted  hydrogen  water,  how 

prepared  and  kept,  151. 
Sulphuric  acid,  as  reagent,  150. 

tests  for,  93. 
Sulphurous  acid,  90. 
Sulphur,  precipitation  of,  22,  31. 

Table  for  Class  I,  22. 


Table  for  Class  II,  29. 

III,  39. 

IV,  53. 

V,  62. 

VI,  68. 

the  separation  of  the  seven 
classes  of  metallic  ele- 
ments, 75. 
Table  of  solubilities,  128,  129. 

the  seven  classes  of  metallic 
elements,  17. 
Tartaric  acid,  as  reagent,  151. 

tests  for,  75. 
Tartrates,  tests  for,  95. 
Test-tube  rack,  164. 
Test-tubes,  163. 
Thiosulphates,  tests  for,  90. 
Tin,  a  member  of  Class  III,  11,  32. 
confirmatory  test  for,  38. 
converted  into  an  insoluble  ox- 
ide by  HNO3,  34. 
globule,  described,  112. 
presence  of,  indicated,  42,  43. 
reduction  of,  by  zinc,  38. 
see  sulphide  of. 
test  for,  38. 
Triangle,  178. 
Tripod,  178. 

Utensils,  list  of,  162. 

Water,  158. 
Water-bath,  179. 
Wash-bottle,  184. 
Wire-gauze,  178. 

Zinc,  a  member  of  Class  V,  13,  58. 
as  reagent,  157. 
precipitated   as    sulphide,  13, 

58,  60. 
presence  of,  indicated,  63. 
confirmatory  test  for,  60. 


QDSS   Eliot,  C.W.      48515 
E42n     The  compendious  manual  of 
1892     qualitative  chemical  anal- 
ysis^  16th  ed. 


>.:'iy       f  ' 


